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My PH and CO2 levels fluctuate a lot from morning when the lights go on to evening when they go off again. PH swings from 6.50 to 6.25, but CO2 seems to be the bigger fluctuation where it takes a few hours into the day before it reaches optimal levels (Drop checker goes lime green).

Would it be better to use a PH Controller and keep a constant level of PH6.25 where CO2 is at a optimum and get the most of plant growth during the time lights are on?

Currently I have CO2 switch on 2 hours before lights, but it still doesn't seem to reach Lime Green in drop checker until later in the day. If i switch it on earlier it just means the levels go high quickly and CO2 ends up being too high by the time the day is over.

There seems to be a lot people talking against PH Controllers though.. (other than the price).
 

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I use my controller to get to my target CO2 quicker. The solenoid is on a timer though and shuts it off one hour before lights out and comes on one hour before lights on. You don't need to worry about pH swings due to CO2. You want to see a swing of .5 to 1 each day IMO. A controller is not a necessity though-it's a luxury.
 

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I have the exact same problem and I'm trying to figure out how to handle it. I'm considering getting a ph controller, too.

My observation from reading this forum is:

1) many people say that you don't need a ph controller, but nobody explains exactly how to get a stable/good CO2 level without one

2) larger tanks seem harder to get the levels right

3) with all the talk about how easy and safe CO2 is, I read about someone gassing their fish on a regular basis. so a ph controller may be an important safeguard and not just a luxury
 

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If you can find a way to set up a pH controller so it actually does maintain a constant level of CO2 in the tank, during the photoperiod only, it could be a good thing. But, the pH in the water doesn't track the ppm of CO2 instantly. There is a lag there too. And, any controller has to allow the pH to vary a little in order to work. Otherwise, it continually hunts - turns on and off every few seconds - which isn't a great idea either. As far as I know most pH controller have a "on" setting and a different "off" setting, to avoid the hunting.

You can't use a drop checker to track how well the pH controller is working, because of the 2 hour lag in response of the drop checker. It just isn't easy to measure/control CO2 without spending a fortune on equipment.

It shouldn't take an hour to get the tank up to the desired level of CO2. You can work on the CO2 delivery/diffusing system to get that time period much shorter, but you will always have a big uncertainty in how much CO2 is in the water, unless you buy some very expensive measuring equipment. Even then, you aren't going to be able to pinpoint the ppm of CO2, because it varies widely around the tank, depending on water circulation, plant uptake rates, loss from the water surface, etc.

Consider reducing the light intensity so the needed ppm of CO2 is low enough to let you safely run it 24 hours a day. Then, the concentration will be a lot more uniform, increasing a bit at night when the plants stop using it, and going back down a bit during the day as the plants start using it.
 

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If you can find a way to set up a pH controller so it actually does maintain a constant level of CO2 in the tank, during the photoperiod only, it could be a good thing. But, the pH in the water doesn't track the ppm of CO2 instantly. There is a lag there too. And, any controller has to allow the pH to vary a little in order to work. Otherwise, it continually hunts - turns on and off every few seconds - which isn't a great idea either. As far as I know most pH controller have a "on" setting and a different "off" setting, to avoid the hunting.

You can't use a drop checker to track how well the pH controller is working, because of the 2 hour lag in response of the drop checker. It just isn't easy to measure/control CO2 without spending a fortune on equipment.

It shouldn't take an hour to get the tank up to the desired level of CO2. You can work on the CO2 delivery/diffusing system to get that time period much shorter, but you will always have a big uncertainty in how much CO2 is in the water, unless you buy some very expensive measuring equipment. Even then, you aren't going to be able to pinpoint the ppm of CO2, because it varies widely around the tank, depending on water circulation, plant uptake rates, loss from the water surface, etc.

Consider reducing the light intensity so the needed ppm of CO2 is low enough to let you safely run it 24 hours a day. Then, the concentration will be a lot more uniform, increasing a bit at night when the plants stop using it, and going back down a bit during the day as the plants start using it.
The Milwaukee controller can be set to have a swing between the on and the off ph so that shouldn't be a problem. My drop check is one of those tiny ones and it seems to read in well under an hour, so that will help. I have reduced surface agitation to reduce loss from the surface.

I'm doing everything I can do stabilize the CO2 but I just can't seem to get there!
 

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It shouldn't take an hour to get the tank up to the desired level of CO2.
At 6 bubbles/second it takes 2 or 3 hours to get the drop checker into a nice green - at least! I first checked for leaks in the system. I have a clear PVC reactor so I can actually see the bubbles being injected into the reactor (which is super cool) and the bubbles coming into the reactor match exactly the bubbles in the bubble counter. So, no apparent leaks in that part of the system.

Inside the reactor I see a swirling mess of bubbles at the top of the clear tube. The vast majority of these bubbles bounce around and around at the top, but only a nominal amount make it out through the bottom. If I look at the filter output, I'll see a tiny CO2 bubble shoot out every 2 or 3 seconds. This suggests to me that the CO2 is dissolving almost completely in the reactor before it's send into the tank. So, no apparent issues with diffusion/dissolving the CO2.

I've moved the DC all around the tank. I am confident the circulation pattern in the tank is slow, steady, and covers the entire tank. When I used a diffuser I was able to follow the bubbles just about everywhere and over a period of 10 minutes even the more dead spots in the tank had bubbles cruising through. So, I am fairly confident that tank circulation is good and the drop checker hasn't' been in a dead spot.

The incredibly helpful Orlando from GLA, who sold me the regulator, is always willing to help out. He asked a series of questions including about surface agitation. I did have a powerhead aimed slightly upward, causing an area of roughness and ripples along the surface. No whitewater or bubbles, but heavy rippling 24 hours a day. He suggested that the surface agitation may be too much so I reduced it massively today. Now the surface has a very gentle swirl to it but for the most part its calm and flat. We'll see how much that helps.
 

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Hoppy,

Great info as always. One thing that I still haven't grasped though. I hear run the co2 24/7. Then hear that there is no need for that, just have the co2 kick on a little before lights on. Then here that there is also no need for that, just put the lights and co2 on the same timer.

Let's pretend that we all have a good idea about lighting and have low to medium lights.

Do co2 fluctuations during lights out effect BBA?

I can understand why folks get confused(as do I). I know that no 2 tanks are the same and it's a matter of trial and error.

There probably isn't one answer for this but still would be interested in what some experienced folks(like yourself) have to say.
 

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Even then, you aren't going to be able to pinpoint the ppm of CO2, because it varies widely around the tank, depending on water circulation, plant uptake rates, loss from the water surface, etc.
Always trust the people who are the most caution and the least dogmatic with their advice, I say :)
 

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Stuff I've used

American Marine Pinpoint Controller, down flow reactor, drop checker. Reconstituted RO water 2ppm before adding GH, KH mineral salts back setting parameters, 75g tanks.
The controller has two plugs one for low point active (air or power bubbler (I don't use it)) and high point active (CO2 injection solenoid) with both shutting down at center point so I'm controlling over only half the range. With a 0.4pH range that holds to a 0.2pH range +- the reaction swing on the low side. When I've checked this is very rarely far enough down to activate the low side plug. Been using two units for >yrs. and like them. The bubble rate is beyond counting into the reactors and it drives the pH down within 15 minutes averaged on a 75g tank. The solenoid 'click' can be heard from within the cabinets about 2-3 cycles an evening.

The down side to this setup is if the solenoid fails or sticks open I'll gas my tanks in short order.
I don't believe you can get much closer than that to a steady ppm using automated equipment without the steady cycle Hoppy referred too.

hope this makes sense
 

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Having already experienced a solenoid failure, any reference to a solenoid failure makes me nervous! Thankfully, my CO2 failed in the closed position while I was overseas for 5 weeks and I had to deal with an algae outbreak rather than a bunch of dead fish.

I wonder if I could simply introduce an ph controller as another mechanism to help control this. I would still leave the whole system on a timer. I do like leaving my bubbler on at night, it changes up the circulation in the tank quite a bit which seems to be very good for the plants/fish.
 

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The solenoids I have spring closed as do most under failure conditions.
 

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How long is the cord that leads to the probe on that ph controller?
 

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I think the cable is 10'

Yup just checked
American Marine PINPOINT pH Replacement Probe 10 foot cord Ag-Ag/Cl reference Extended life High supression cable jacket
 

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The co2 flux doesn't matter in terms of not having a constant co2 level at night. I think enough folks have successful tanks across a wide variety of conditions without a controller to put this past debate.

I don't think providing co2 at night is doing anything. You could provide all the co2 you want and if the plants aren't photosyntheising you will still get algae. The co2 flux itself is not causing the algae issues.

Many, if not most here change a large amount of their water weekly. The result is a huge co2 shift sometimes right in the middle of the day. So whether you use a co2 controller or not you will still get this shift until the co2 adjusts. I've never seen any problems associated with this and this is during daylight hours. So I wouldn't worry about a co2 drop at night or even if it takes the tank a few hours after lights on to get to good levels. If your having issues look to your organic load and lights.
 

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Don't forget, the pH probe needs recalibrating periodically.

As far as I know, the drop in CO2 concentration with lights out doesn't lead to a BBA outbreak. It is what happens during the time the lights are on, and how consistent it is from day to day that is important - as far as I know.

When you use a high bubble rate, with an external "Rex" reactor, with a pH controller, you will necessarily get a big overshoot on CO2 concentration. The CO2 collected in the reactor will continue to go into the water until it is depleted, some time after the controller shuts off the CO2. And, again, the water pH changes lag the CO2 concentration changes, further adding to the overshoot.

But if you use a low bubble rate, the controller is mostly just a safety feature, shutting down the CO2 before it gets too high in the tank. A happy medium seems to be desirable?
 

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For what it's worth, I've recently considered the possibility of using a PH controller together with a Drop Checker, in order to get the best of both worlds and automatically control my CO2.

Turns out this would be either expensive or inaccurate, as explained by Hoppy and others: the DC has a long delay and the controller would end up always under/over shooting the target concentration, unless a gas-permeable membrane is used to reduce the delay in reading PH from the control solution.
 

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For what it's worth, I've recently considered the possibility of using a PH controller together with a Drop Checker, in order to get the best of both worlds and automatically control my CO2.

Turns out this would be either expensive or inaccurate, as explained by Hoppy and others: the DC has a long delay and the controller would end up always under/over shooting the target concentration, unless a gas-permeable membrane is used to reduce the delay in reading PH from the control solution.
Certainly it would be more expensive, but it's hard to imagine that it would be less accurate than the information that I already have. I'm dealing with ambiguous parameters, hardly any reference or examples of similar tank settings, and a drop checker that reads an hour or so late.

Adding a ph controller would at least give me one more reading, inaccurate as it is :). Also, I am increasingly convinced that the CO2 systems aren't as rock-solid as advertised. This week I met yet another person who gassed her fish! So, at the very least the ph controller could provide some protection against that.

I understand and appreciate all of this input.

But, where does this leave me?


  • With a low bubble count, my dc never gets to a nice green.
  • With a medium bubble count, my dc is blue when the lights come on and green when they go off.
  • With a high bubble count, I can start the CO2 hours before the light comes on and it will be green when they do, then I have to shut the CO2 down hours before the light goes off.

So, I'm not able to get a clear understanding of what people are doing, especially with regard to bubble rate, tank size, and timer settings. Clearly every tank is different, but I'm not having any luck stabilizing my CO2.

Orlando's comment that I may have too much surface agitation makes sense. That would mean that I need a high bubble count to offset the outgassing from the surface agitation, and that high bubble count makes the whole thing harder to make stable.

What kind of surface agitation do any of you have? Have you noted that with a rippling surface on the water, much CO2 is lost?
 

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UPDATE: With the surface agitation reduced substantially, the drop checker reached a lime green color much earlier than it did yesterday. This is consistent with the idea that the CO2 was outgassing too much from the turbulent surface. Very encouraging to me, because it seems like a lower bubble rate is going to be easier to control overall.

I've reduce the bubble count by about 50 percent and will attempt to configure the timer/bubbles again over the next couple of days.

I am still liking the idea of a ph controller just for safety, but hey I always like a fun gadget!
 

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it's hard to imagine that it would be less accurate than the information that I already have.
Yes, true. What I meant is controlling when the CO2 valve turns on & off by means of a PH controller -> that is inaccurate. If the probe in the water column, then it's not only measuring CO2, but all the other factors that affect the PH. If the probe is in a drop-checker solution, then it's delayed by an hour or so and will toggle the CO2 valve too late relative to current CO2 levels.

Apologies, I'm not bringing anything new to the table... back to you now :p
 

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The solenoids I have spring closed as do most under failure conditions.
Mechanical failure, contamination in the plunger area or worn spring can cause it to fail open. If it was electrical failure then yes it would be closed during failure.
 
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