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I'm new to CO2 and will be adding Endlers, RCS, and Amanos shortly to a newly started 50g, gradually of course while it cycles. It's dawning on me that CO2 is by far the most dangerous aspect of fishkeeping, where a simple mistake or fault in a number of systems can quickly kill your entire tank.

The two main critical risks I see are(1) CO2 does not stop after lights out and (2) too much CO2 is delivered to the tank when lights are supposed to be on. In both scenarios, my assumption is that if you are targeting 30ppm, which sounds like it is close to the asphyxiation point for fish/critters, after just a few hours in failure mode, all animal life in your tank is dead.

For the first risk, that CO2 does not stop after lights out, I plan to mitigate by using two battery backed up timers in serial. This way if power fails, the timers retains both accurate time and programming. By using two in serial, if one timer fails to cut power at lights out, the other timer will also cut power at the same time so CO2 power will still be cut. I'm also considering running an airstone after lights out that not only brings more O2, but will would help mitigate if CO2 kept flowing through some fault. I feel pretty good about mitigating this risk scenario.

For the second risk, that too much CO2 is delivered to the tank when lights are supposed to be on, I am less certain about my mitigation strategies. There would be a number of root causes for such an event:
1. operator error messing with regulator valve setting
2. accidentally bumping a regulator valve and opening it more
3. regulator malfunction
4. lights fail to come on

I'm not sure how to easily mitigate root causes (3) and (4) above. I know regulators are pretty reliable but they do break. I'm using a Fluval LED 3.0 which is pretty resilient and has its own 24 hour cycle which I like. But as someone who works in tech there is plenty that could go wrong such as a light firmware update that messes up schedule or operation, power outage that wipes/changes the light config/schedule, and operator error such as accidentally unplugging or changing settings.

Mitigation strategies I have considered for this risk scenario are:
1. Explore a pH controller that can turn off CO2 at a low pH setting. I understand these are expensive and unreliable but maybe if used just as a safety device and not a full time controller, it would be more reliable.
2. Explore using a photocell relay controller (these look cheap!). This would power on CO2 ONLY after the photocell sees light coming from the light fixture (would have to mount just below fixture). Of course this means CO2 can't get a head start before lights on but I could live with that.
3. Run at 20PPM CO2 or some amount lower than 30PPM which is apparently right on the line of death for the tank critters. This way there is more time to react and would take longer to kill all the fish. I think I could live with this. I'm not looking to enter an aquascape contest or get super fast growth at all costs. I got CO2 so I could try some high light and carpeting plants. 20PPM is still an order of magnitude more CO2 than nominal so perhaps that is enough. I am also dosing Excel.
4. For CO2 valve setting security, explore ways to lock down the valves (e.g. a cheap way I've seen in research facilities would be to tape them at their settings so they can't be easily moved accidentally)

Are there any other mitigation strategies for this possible failure scenario or anyone have experience with the ones I enumerated above? Am I worrying too much about this?
 

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Besides a pH controller, I use a Kasa smart strip that runs a powerful air pump for the last 10 minutes each hour, and then all night while the CO2 is off. Only set them up this way in January but it's worked for me without a hitch so far.
 

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You may be over-thinking this. I do not recall seeing any complaints about high-quality solenoids freezing open, although it is possible. Your relayed timers would certainly address some of the backup issues. However, if a timer fails in the “on” position, then you are down to the one-timer-only mode anyway, and may not be aware of it, unless you intend to verify operation regularly ...but then there’s that nagging Murphy’s law about “If it can wrong, it will.”

A dual stage (not gauge) regulator should prevent an EOTD event, if that is a concern and they do provide, generally, that increased backup-in-depth aspect.

You can also run CO2 24/7 (I do) and do it without any problem. In fact, I believe it to be beneficial and it actually reduces overall CO2 consumption.
Maintaining good gas exchange is always important regardless of CO2 overdosing concerns, but it should be done via surface agitation and airstones aren’t that effective at doing so. Better to use a pump or skimmer.
 

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Mitigation strategies I have considered for this risk scenario are:
1. Explore a pH controller that can turn off CO2 at a low pH setting. I understand these are expensive and unreliable but maybe if used just as a safety device and not a full time controller, it would be more reliable.
Not sure where you heard this, but good quality CO2 controllers like Milwaukee and American Pinpoint Marine are rock solid.

I've used one full time during the CO2 period for years. IMO, makes it easier to dial in CO2, and acts as a fail safe protecting fish. With a tank full of mature and hard to replace Rainbow fish, that means a lot to me.

Like @Blue Ridge Reef above, I use a Kasa Smart Strip to turn on bubbler about 10 minutes per hour to help keep oxygen levels up.

As to running CO2 24/7, I'm not convinced it makes a difference either way. Personally I don't run CO2 overnight as it seems like a waste of gas. Of course, I'll admit I've never run it 24/7, so can't say for sure if it makes any difference.
 

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Once we get past the idea of hobby expense, (what a joke!) I find the best way to add a layer of safety is the PH controller and it has several other factors that I like. Anybody here who thinks it is actually practical has a shock coming!
I find all my fish can do better if things are stable. Many argue that the natural world is not stable but that ignores the amount of freedon fish have to move to the conditions they find better.
One way to get to the stable point is to let a controller hold the PH stable. I do it 24-7 and find it easy. Added benefits start with ease of gradually working the CO2 amount down by some small amount like .2 a day until reaching what I want or seeing fish begin to struggle.
To somewhat offset the price of controllers, I can use a simple, single stage regs, paired with good quality Clippard Mouse solenoids and needle valves while feeling sure the controller will stop any overgassing, at least in most cases.
I CAN still screw it all up and try to kill all the fish but it is not the fault of the equipment! It's not foolproof as there is no such thing when humans are involved but it has always worked out real well.
 

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@Blue Ridge Reef, @Greggz and @PlantedRich,

You swear by pH controllers, and I have no direct experience with them, but how do you deal with the KH shift throughout the week? Do you add bicarbonate along with your regular nutrient dosing to keep pH and CO2 stable? My KH drifts from above 4 to ~3, or less, during a week or two. This would result in a 10ppm swing of CO2, for me, if I were to focus on a strict pH level. I have to add more bicarbonate after every water change to accommodate this drift in order to hit my ~6.5 pH starting target. Some people may have the opposite problem of rising KH levels. I do recall that one, or more, of you are bottoming out on KH, so that may not be an issue for those of you that are.
 
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@Blue Ridge Reef, @Greggz and @PlantedRich,

You swear by pH controllers, and I have no direct experience with them, but how do you deal with the KH shift throughout the week? Do you add bicarbonate along with your regular nutrient dosing to keep pH and CO2 stable? My KH drifts from above 4 to ~3, or less, during a week or two. This would result in a 10ppm swing of CO2, for me, if I were to focus on a strict pH level. I have to add more bicarbonate after every water change to accommodate this drift in order to hit my ~6.5 pH starting target. Some people may have the opposite problem of rising KH levels. I do recall that one, or more, of you are bottoming out on KH, so that may not be an issue for those of you that are.
This is a valid point.

When I was using sand, KH was never an issue as it was rock solid.

With the soil my pH drifts down a bit too. But for me, it's really only from about 1.0 to close to zero. So my pH right after a water change is 6.40. I set the pH controller for 4.95. Degassed drifts down to only about 6.30 by the end of the week. So in my case, my peak pH drop goes from 1.45 to 1.35 by the end of the week. Nothing for me to worry about.

With any method of controlling CO2, it's a good idea to keep an eye on your KH. Sometimes it can change seasonally quite a bit. The lower the KH is, the less CO2 it will take to drop the pH. And the higher the KH, the more CO2 that will be required for the same relative drop. So in my opinion, either way you need to be aware of KH fluctuations.
 

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I wish that alkalinity controllers weren't $1,000.

I would also imagine that active substrates would turn pH controllers into a nightmare.
 
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@Blue Ridge Reef, @Greggz and @PlantedRich,

You swear by pH controllers, and I have no direct experience with them, but how do you deal with the KH shift throughout the week? Do you add bicarbonate along with your regular nutrient dosing to keep pH and CO2 stable? My KH drifts from above 4 to ~3, or less, during a week or two. This would result in a 10ppm swing of CO2, for me, if I were to focus on a strict pH level. I have to add more bicarbonate after every water change to accommodate this drift in order to hit my ~6.5 pH starting target. Some people may have the opposite problem of rising KH levels. I do recall that one, or more, of you are bottoming out on KH, so that may not be an issue for those of you that are.
In my case, I have so much limestone that it winds up only being a very small part that is changed. Never really been able to see any KH change. It might change but it takes so much to even get a reading on KH, that I no longer keep the kit. I no longer even do enough thinking on KH to remember what it last read in PPM, etc. but I did just change out my home water softener and reset it for 21 grains of hardness, but that's a different scale! doing the math that works out somewhere around 350 PPM, so a loos of a few is not significant.
One reason for me to not try to fight it is the experience we have had with pool water and finding it really, really hard to change it and keep it steady and pool water is somewhat like the tank in that it is easier if you keep it stable at whatever level works. One of the better moves we made was doing away with the pool !!
 

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I would also imagine that active substrates would turn pH controllers into a nightmare.
Yeah could be. Much depends on the initial KH and how much it drops.
@Deanna you may find this interesting.

Before I went to RO water, my KH was about 15 and degassed pH was about 8.0. I went through a 10 lb CO2 every 8 weeks. Almost like clockwork.

When I went to RO with very low KH, the same 10 lb tank with the same relative pH drop lasts 18 weeks.

So IME, no question that the same amount of CO2 will create a different relative pH drop depending on KH. So again, either way, pays to keep an eye on KH.

I remember quite a while ago I mentioned this to @Immortal1. Turns out he was having some issues with his tank, and turns out his tap KH had changed quite a bit.

So to me the moral of the story is, if you see anything wonky in a high tech tank, the first thing I always double and triple check is KH, degassed pH reading, and pH drop. It can save you from banging your head against the wall chasing other solutions. Many times it's just getting CO2 dialed in (like Tom Barr has said a million times!).
 

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Discussion Starter · #12 ·
You may be over-thinking this. I do not recall seeing any complaints about high-quality solenoids freezing open, although it is possible. Your relayed timers would certainly address some of the backup issues. However, if a timer fails in the “on” position, then you are down to the one-timer-only mode anyway, and may not be aware of it, unless you intend to verify operation regularly ...but then there’s that nagging Murphy’s law about “If it can wrong, it will.”

A dual stage (not gauge) regulator should prevent an EOTD event, if that is a concern and they do provide, generally, that increased backup-in-depth aspect.

You can also run CO2 24/7 (I do) and do it without any problem. In fact, I believe it to be beneficial and it actually reduces overall CO2 consumption.
Maintaining good gas exchange is always important regardless of CO2 overdosing concerns, but it should be done via surface agitation and airstones aren’t that effective at doing so. Better to use a pump or skimmer.
I was thinking of using two timers in serial, one timer backs up the other. Both have to be on for CO2 to be on. I have the CO2Art regulator which is a dual stage. I have seen people post that their regulator "got stuck" but I'm guessing a very rare occurance.

I have to missing something, I didn't think it was possible to run CO2 24/7 with animals in the tank! I assumed once lights are out, with CO2 running they are asphyxiated within hours due to build up of CO2, which is why I am so concerned about having a lot of safeties in place. Same with if lights don't come on and CO2 does. I'm assuming at 30ppm, your tank animals are one minor "oops" away from a tank kill since people note that a little higher and their fish have trouble breathing.

24/7 would waste gas, but one side benefit is it avoids the daily pH swing which I know people say doesn't bother their animals but I am skeptical its a healthy thing. 1 pH drop/rise is a 10x increase/decrease in acidity. Good food for though although I need to understand CO2 levels a little more.

Besides a pH controller, I use a Kasa smart strip that runs a powerful air pump for the last 10 minutes each hour, and then all night while the CO2 is off. Only set them up this way in January but it's worked for me without a hitch so far.
That's an interesting idea. Does it expel all the CO2 gas in that 10 minutes and create a pH swing every hour?

Not sure where you heard this, but good quality CO2 controllers like Milwaukee and American Pinpoint Marine are rock solid.
I've used one full time during the CO2 period for years. IMO, makes it easier to dial in CO2, and acts as a fail safe protecting fish. With a tank full of mature and hard to replace Rainbow fish, that means a lot to me.
That's good to know they are reliable! A couple articles I read indicated they end up switching on an off too rapidly. My experience with pH probes in a lab and with owning a Hanna I was using for hydroponics is the pH probe is the weak point and needs to be well maintained and calibrated, replaced every so often. I remember in the lab seeing them "drift" when they started to go bad. Of course part of the issue is taking them out of the solution and letting them dry, that's what kills them early so maybe sitting in the aquarium water full time keeps them accurate and functional.

Also I am using lots of Seiryu stone and have noticed a KH drift from 4dKH to 7dKH within 4 days. So per another poster's comment, I wonder how that weekly drift would play on a pH controller.
 

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Just wanted to bump the value of gas exchange as a couple posters mentioned before me. This is like your airstone mitigation idea but at even a higher level. It is one of the best "risk mitigation" steps by off gassing any excess co2 via surface agitation and loading up your tank with good oxygen levels to allow for even higher levels of co2 injection. I can't say that I've measured mine by any real scientific co2 meters nor most people on here, but I highly suspect some to be pushing beyond 30ppm easily without drama. Mechanical methods to limit co2 disasters are all good, but there's some solid value in simply "encouraging" nature to do its thing.


You may want to spend some time here:

https://www.advancedplantedtank.com/blogs/choosing-co2-why/how-to-push-the-limits-of-co2-safely

He used to have this video linked in there too, but I guess he reorganized some stuff:


and also the main co2 page and ... well. that entire site, really :)
 

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I have to missing something, I didn't think it was possible to run CO2 24/7 with animals in the tank! I assumed once lights are out, with CO2 running they are asphyxiated within hours due to build up of CO2, which is why I am so concerned about having a lot of safeties in place. Same with if lights don't come on and CO2 does. I'm assuming at 30ppm, your tank animals are one minor "oops" away from a tank kill since people note that a little higher and their fish have trouble breathing.

24/7 would waste gas, but one side benefit is it avoids the daily pH swing which I know people say doesn't bother their animals but I am skeptical its a healthy thing. 1 pH drop/rise is a 10x increase/decrease in acidity. Good food for though although I need to understand CO2 levels a little more.
Absolutely possible and many of us do it. As @ipkiss mentioned, the key is excellent gas exchange. I use a skimmer to reach O2 saturation and it provides plenty of elasticity for fauna stress from CO2 movement, but there is no CO2 movement. The excellent gas exchange also works to maintain a stable CO2 level and that stability is important to minimize algae and enhance plant health. My CO2 levels, as measured by pH, are rock solid day and night, due to the gas exchange. You actually don't get a CO2 build-up at night. That means no variability, which reduces stress on the flora and fauna. The "oops" factor is actually lowered. Remember that pH is logarithmic. If a controller is set to pH of 6.5 and varies by just 2/10 point (which a drop in KH will force upon it), and your dKH is 3, your CO2 can jump from 28ppm to 45ppm. You better have good gas exchange to handle that.

Contrary to what seems intuitive, you actually use less gas by running 24/7. I suspect that it is due to not having to drive so hard to reach saturation every morning, which also can cause higher than desired levels toward the end of the photoperiod. There are also other benefits.
 
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Absolutely possible and many of us do it. As @ipkiss mentioned, the key is excellent gas exchange. I use a skimmer to reach O2 saturation and it provides plenty of elasticity for fauna stress from CO2 movement, but there is no CO2 movement. The excellent gas exchange also works to maintain a stable CO2 level and that stability is important to minimize algae and enhance plant health. My CO2 levels, as measured by pH, are rock solid day and night, due to the gas exchange. You actually don't get a CO2 build-up at night. That means no variability, which reduces stress on the flora and fauna. The "oops" factor is actually lowered. Remember that pH is logarithmic. If a controller is set to pH of 6.5 and varies by just 2/10 point (which a drop in KH will force upon it), and your dKH is 3, your CO2 can jump from 28ppm to 45ppm. You better have good gas exchange to handle that.

Contrary to what seems intuitive, you actually use less gas by running 24/7. I suspect that it is due to not having to drive so hard to reach saturation every morning, which also can cause higher than desired levels toward the end of the photoperiod. There are also other benefits.
I'm another person who runs CO2 24/7 using an American Marine Pinpoint controller. Once you have it set and running for a bit, it's reliable. I'm of the camp that thinks the fewer things vary in the tank, the better, so my ph swing is small < 0.2. I do double check my ph with a test kit to make sure that what the controller is reading is close to what the test kit reads.

AFA kh swings. I had a couple when I first set up the tank, added a bit of baking soda to get the reading up. After a bit, it stabilized. I wonder if it has anything to do with adding a cuttlebone to the tank for the snails? If you're dealing with low kh tap water, you can always add a bit of aragonite or crushed coral to your filter as a buffer.
 

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Discussion Starter · #16 ·
Just wanted to bump the value of gas exchange as a couple posters mentioned before me. This is like your airstone mitigation idea but at even a higher level. It is one of the best "risk mitigation" steps by off gassing any excess co2 via surface agitation and loading up your tank with good oxygen levels to allow for even higher levels of co2 injection. I can't say that I've measured mine by any real scientific co2 meters nor most people on here, but I highly suspect some to be pushing beyond 30ppm easily without drama. Mechanical methods to limit co2 disasters are all good, but there's some solid value in simply "encouraging" nature to do its thing.


You may want to spend some time here:

https://www.advancedplantedtank.com/blogs/choosing-co2-why/how-to-push-the-limits-of-co2-safely

He used to have this video linked in there too, but I guess he reorganized some stuff:
https://www.youtube.com/watch?v=alTRKo8-jeM


and also the main co2 page and ... well. that entire site, really :)
I've been all over that site for a couple weeks, it is such a good site! That video was new to me. It is excellent and gave a lot of information. I feel much better having seen it. I have two 200GPH Aqueon canisters on this 50G (I have Endlers - great at overstocking themselves). Almost all of my plants sway gently in the current so I know there is good flow from top to bottom. My surface agitation looks almost as vigorous as his in the video.

I could not figure out why people are using skimmers on their freshwater tanks but the vid cleared that up. I love the idea. It cleans the surface, which solves air exchange and water chemistry issues, AND does a bonus super O2 injection while doing it. Buying one tonight.

Absolutely possible and many of us do it. As @ipkiss mentioned, the key is excellent gas exchange. I use a skimmer to reach O2 saturation and it provides plenty of elasticity for fauna stress from CO2 movement, but there is no CO2 movement. The excellent gas exchange also works to maintain a stable CO2 level and that stability is important to minimize algae and enhance plant health. My CO2 levels, as measured by pH, are rock solid day and night, due to the gas exchange. You actually don't get a CO2 build-up at night. That means no variability, which reduces stress on the flora and fauna. The "oops" factor is actually lowered. Remember that pH is logarithmic. If a controller is set to pH of 6.5 and varies by just 2/10 point (which a drop in KH will force upon it), and your dKH is 3, your CO2 can jump from 28ppm to 45ppm. You better have good gas exchange to handle that.

Contrary to what seems intuitive, you actually use less gas by running 24/7. I suspect that it is due to not having to drive so hard to reach saturation every morning, which also can cause higher than desired levels toward the end of the photoperiod. There are also other benefits.
I'm almost sold on this concept of 24/7 CO2. The stability it brings is very appealing and I feel better about it now that I did a mini education in gas exchange. One fly in the ointment, I used a hearty portion of Seiryu rock and it appears that it will create a KH drift between water changes. Do you have to continuously alter bubble count to chase a KH drift? One idea I had for this is to buffer up the water at water change. The Seiryu dissolves in a weak acid so if I can push the starting pH higher, maybe it won't dissolve or as much.
 

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I'm almost sold on this concept of 24/7 CO2. The stability it brings is very appealing and I feel better about it now that I did a mini education in gas exchange. One fly in the ointment, I used a hearty portion of Seiryu rock and it appears that it will create a KH drift between water changes. Do you have to continuously alter bubble count to chase a KH drift? One idea I had for this is to buffer up the water at water change. The Seiryu dissolves in a weak acid so if I can push the starting pH higher, maybe it won't dissolve or as much.
No: CO2 does not significantly affect KH (it's negligible). If running 24/7, the amount of CO2 you establish in your tank remains fixed as a function of your delivery system, gas exchange and plant consumption, the former two having the most impact, by far. Using pH controllers (with varying KH levels) and/or timing solenoids to inject at certain times of the day create much more variability in CO2.

Incidentally, I'm not trying to convince you to go 24/7. It is simply another legitimate option, particularly if you are concerned about stable gas levels. I would guess that far more people use the CO2 timing approach than run 24/7 and they have no problems. However, I have often wondered how many "How do I get rid of this algae?" postings would disappear if CO2 were run 24/7 with good gas exchange.
 
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There is only one thing controlling the CO2 that enters the tank. Its the needle valve. Get a good quality one. This will prevent 99% of the problems. keep the Co2 setup in a cabinet and lock it up once it is set. If you can do this, it will stop any one accidentally messing up with the controls. I lock mine up.

When you use 2 or 3 bps you will not suffocate the fish, whether the lights are on or off.

I differ with the general opinion that surface agitation is bad and most of the gas will escape. All my planted tanks have ample surface agitation that happens normally from the filter output. There is still sufficient CO2 remaining that the plants grow well.
 

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That's an interesting idea. Does it expel all the CO2 gas in that 10 minutes and create a pH swing every hour?
Not all by any means, but over half. But these swings don't seem to impact livestock, I keep some pretty fragile Caridina shrimp in one of mine that would wipe out if such a swing were done via water change. But the osmotic pressure is stable when pH drops from carbonic acid from CO2 and this has been explained to me as to how full point pH swings can be done without stressing your fauna. My source water is +/- 1.5dKH out of the tap, and creeps downwards over time. I try to do 50% water changes weekly, but even if I skip a week the KH is still 1 dKH (according to a cheap API kit anyway). It's not the pH change that causes problems when too much CO2 is delivered, it's too much CO2/too little O2.
 

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Contrary to what seems intuitive, you actually use less gas by running 24/7. I suspect that it is due to not having to drive so hard to reach saturation every morning, which also can cause higher than desired levels toward the end of the photoperiod. There are also other benefits.
Can you elaborate on this? Maybe I am missing something.

For a few months I was not using my controller, just dialing CO2 in via flowmeter.

After much trial and error I had my flow rate set to 40 cc/min. At that rate, takes about two hours for pH to hit peak, then pretty much stays right there for the entire lighting period. So I had CO2 coming on two hours before light, then going off one hour before lights go off. The total CO2 injection time was 9 hours. I should note that I also have constant pretty vigorous surface agitation 24/7.

Running constant injection rate of 40 cc/min for 9 hours = 21,600 cc of CO2.

Running constant injection rate of 40 cc/min for 24 hours = 57,600 cc of CO2.

I'm not trying to be argumentative, I just don't understand what you are getting at or how that can be? Again, maybe I am missing something?
 
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