Co2 adjustment question - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 05-04-2020, 09:41 AM Thread Starter
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I've had great growth since setup but I periodically get algae which a tiny co2 boost gets rid of. Then the plants get bigger and I have to push it harder and so on. Problem is now that it's working okay that the ph KH chart says I'm at 46ppm... well I doubt that so I'm assuming my kh or ph has other contributing factors. So I bought a drop checker with 4dkh ready to use fluid to get a rough idea. It goes yellow about 3-4 hours into my Photoperiod. So now I'm concerned maybe I am overdosing long term. Fish seem fine so I'd say I can't be but I'd like to know really. Having realised how these are basically useless in large aquariums I need to rethink.

As I understand it I can use a 1.2ph drop to estimate the recommended 30ppm

But I don't get how to do this. Where do I take my baseline? The tank despite the airstone overnight is still showing a dark green Drop checker the following morning.

Tap ph is 7.6 consistently
Tank ph in the morning just before CO2 starts is 7.2
Tank when running at saturation is 6.6

Beside my main tank is a small tank with same sand, same nutrients ratio and same kind of plant load and fish load per litre. Same water change schedule and percentage. It has no CO2 system. Its PH is 6.6 all the time....

Could someone help me grasp this concept a little better so I can make informed decisions rather than guessing my way through it.

Many thanks.

TANK INFORMATION
I have a 600l tank with co2 injection via a regulator and a huge reactor. I get no bubbles at all. Co2 comes on 2 hours before my lights and goes off 2 hours before my lights. 8hour lighting period and I'm definitely in the high light category. I get 55par in the front corner and 65 in the centre over my grasses. Apowerful air stone runs the entire time the lights are off to off gas and the surface gets a nice ripple from both pumps. Not breaking the surface but good interchange. Flow is coming from 2 FX6 canisters that have their in and outs at opposite sides so I get a figure 8 across them. You can see if I stir up substrate that the distribution is excellent. I'm dosing tnc complete at 5m per 50l every day with a 60% WC weekly. Keeps me at 20ppm pretty solidly. Tank is immaculate.
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post #2 of 8 (permalink) Old 05-04-2020, 07:39 PM
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Fill a glass with your tank water and let it sit out for several days to allow full off-gassing of the CO2. This can be accelerated by putting an aerator in the glass. Measure the pH daily and, once it stabilizes, you'll have the starting baseline. Subtract your fully gassed 6.6 pH reading from that degassed pH.

Drop checkers are rough guides and highly dependent upon your being certain that the solution is 4 dKH (I run mine using a 5 dGH solution). They should be placed in the tank where you would expect the least amount of CO2 to reach. They are also closely tied to the pH KH calculations (charts also reflect this).

The problem with all of this is that you need to make sure that your pH and KH readings are as accurate as possible and it is not really possible to get high precision with the types of testing approaches that we use in our hobby, although they can be improved significantly through calibration, test modifications and moderately higher-priced offerings. Depends upon how deeply you want to go in terms of accuracy.

Simplest is to try to target a 1-1.4 pH drop as described above.
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post #3 of 8 (permalink) Old 05-04-2020, 10:20 PM Thread Starter
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That's very helpful. Thankyou for clarifying this and for such a detailed response. I've already gotten a stabilised tank water reading at 7.4. Given that I'm at 6.6 and it's on the edge of being right from an observation standpoint it seems that I'm actually okay and I could indeed push it up to where I feel it needs to be. Just means my drop checker will be glowing in the dark haha.

Any idea why my almost identical tank with no co2 is so low ph wise? I was going to introduce a co2 kit on there too but it's so low now I'd be afraid to lol. Like I say its absolutely identical.
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post #4 of 8 (permalink) Old 05-06-2020, 07:30 AM
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I dont see why people are so dead set on 30ppm. In my opinion, use as much co2 as it takes to keep algae away. Co2 is the best algae deterrent. As long as your fish are ok, i shoot for a lime green/yellow on my drop checkers. Whwn its at this level, i dont even have to scrape the glass.
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post #5 of 8 (permalink) Old 05-14-2020, 12:54 AM
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I've recently been exploring the same issues you have. Here's my conclusion:

The 4dkh drop checker is nothing more than a pH indicator. If your drop checker is green with a 4 dkH solution, all that means is that your pH is between 6.6 and 6.9 (based on the pH vs dkH chart). It has nothing to do with the amount of CO2 in the tank. 4 dkH is the standard because most people's tanks without CO2 are closer to the 7.6 range. A 1 pH drop would bring you to 6.6, which is when the 4 dkH solution would turn yellow.

If your base pH when you don't have CO2 running is between these values, your indicator will always be green and it's likely that when you add significant CO2 you will run into the yellow range on the drop checker as a 1 pH drop on a 4 dkH solution indicates yellow based on the pH/dkH chart.

Therefore, as stated above, the best way to actually determine the CO2 concentration is to directly measure the pH drop. If you want the drop checker to be more accurate, you either need a lower value dkH solution that corresponds with your reduced pH level, or increase you pH, but obviously that is highly dependent on the type of livestock you have in the tank.

Also, the difference in pH levels between your two tanks is more likely to hardscape. If you've got a higher percentage of wood in the smaller tank, you will have a lower pH because wood tends to make the water more acidic. Conversely, you may have more basic elements (like limestone or crushed corals) in the larger tank that causes the pH to be higher
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post #6 of 8 (permalink) Old 05-19-2020, 12:58 AM
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Co2 adjustment question

Quote:
Originally Posted by stlhokie View Post
I've recently been exploring the same issues you have. Here's my conclusion:



The 4dkh drop checker is nothing more than a pH indicator. If your drop checker is green with a 4 dkH solution, all that means is that your pH is between 6.6 and 6.9 (based on the pH vs dkH chart). It has nothing to do with the amount of CO2 in the tank. 4 dkH is the standard because most people's tanks without CO2 are closer to the 7.6 range. A 1 pH drop would bring you to 6.6, which is when the 4 dkH solution would turn yellow.



If your base pH when you don't have CO2 running is between these values, your indicator will always be green and it's likely that when you add significant CO2 you will run into the yellow range on the drop checker as a 1 pH drop on a 4 dkH solution indicates yellow based on the pH/dkH chart.



Therefore, as stated above, the best way to actually determine the CO2 concentration is to directly measure the pH drop. If you want the drop checker to be more accurate, you either need a lower value dkH solution that corresponds with your reduced pH level, or increase you pH, but obviously that is highly dependent on the type of livestock you have in the tank.



Also, the difference in pH levels between your two tanks is more likely to hardscape. If you've got a higher percentage of wood in the smaller tank, you will have a lower pH because wood tends to make the water more acidic. Conversely, you may have more basic elements (like limestone or crushed corals) in the larger tank that causes the pH to be higher


Hereís a bit of clarification...the ph of the drop checker is independent of the starting ph of your tank water (assuming youíre not filling it with tank water). A properly made 4 dkh indicator solution would be made with distilled water with just carbonates only added. You can make this yourself with baking soda. So there is nothing else in the drop checker to modify pH. Therefore when you add the indicator solution, at average natural atmospheric levels of co2 (between 2-4ppm) the solution will always be blue or very close to it. If itís not blue, either your solution or your indicator fluid is bad.

When you add co2 to your tank water, it off-gasses into the air inside the drop checker at the same proportion that itís dissolved into your water. The ph scale is logarithmic which means that a drop of 1 ph indicates 10x more acidic and vice versa. In your tank the general goal is to inject enough co2 to get roughly 10x more co2 than regular atmospheric dissolved rates (so, 20-40 ppm Vs. 2-4 ppm). If you record the starting ph value of your drop checker, and then put it in your tank and drop that ph value by 1, you have increased the acidity 10x from your starting point, and therefore have 10x more co2 in your tank than you have in the atmosphere. The reason people use 4dkh usually, is simply that the color change of ph solution is easy to see at that level. If it drops by 1 ph it goes from blue to green, if it drops by more than 1 it will start to go from green to yellow.

You donít need a 4dkh solution necessarily as long as you know what color you are starting with, but for instance if you pick your starting color as green, you have to shoot for yellow, and then itís going to be hard to tell if you are overshooting the mark. Or as mentioned if you go for a 5 dkh solution instead, the starting ph will be higher so it starts as a darker blue...if it then gets all the way to a lighter green or to yellow youíre way past where you should be. 4 dkh was simply picked because itís easiest to distinguish the color changes from there as it gets more acidic.

Youíll notice there is no reference to the ph of your tank water in this explanation, because it has no bearing on the drop checker value.

However you accomplish the same thing by testing your tank ph with the co2 injected and then letting it off gas and watching to see how much the ph drops. It just takes a lot longer.

As already mentioned, the ph / dkh chart when used with tank water is only accurate if you have nothing else in your tank affecting the waterís ph other than Kh, which is rarely the case. Nitric acid is produced by fish waste, tannic acid is produced by driftwood and can occur naturally in some tap water, those are two examples that render the scale fairly useless because thereís just not much room for any error there.


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post #7 of 8 (permalink) Old 05-19-2020, 09:29 PM
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Quote:
Originally Posted by CarissaT View Post
Hereís a bit of clarification...the ph of the drop checker is independent of the starting ph of your tank water (assuming youíre not filling it with tank water). A properly made 4 dkh indicator solution would be made with distilled water with just carbonates only added. You can make this yourself with baking soda. So there is nothing else in the drop checker to modify pH. Therefore when you add the indicator solution, at average natural atmospheric levels of co2 (between 2-4ppm) the solution will always be blue or very close to it. If itís not blue, either your solution or your indicator fluid is bad.

When you add co2 to your tank water, it off-gasses into the air inside the drop checker at the same proportion that itís dissolved into your water. The ph scale is logarithmic which means that a drop of 1 ph indicates 10x more acidic and vice versa. In your tank the general goal is to inject enough co2 to get roughly 10x more co2 than regular atmospheric dissolved rates (so, 20-40 ppm Vs. 2-4 ppm). If you record the starting ph value of your drop checker, and then put it in your tank and drop that ph value by 1, you have increased the acidity 10x from your starting point, and therefore have 10x more co2 in your tank than you have in the atmosphere. The reason people use 4dkh usually, is simply that the color change of ph solution is easy to see at that level. If it drops by 1 ph it goes from blue to green, if it drops by more than 1 it will start to go from green to yellow.

You donít need a 4dkh solution necessarily as long as you know what color you are starting with, but for instance if you pick your starting color as green, you have to shoot for yellow, and then itís going to be hard to tell if you are overshooting the mark. Or as mentioned if you go for a 5 dkh solution instead, the starting ph will be higher so it starts as a darker blue...if it then gets all the way to a lighter green or to yellow youíre way past where you should be. 4 dkh was simply picked because itís easiest to distinguish the color changes from there as it gets more acidic.

Youíll notice there is no reference to the ph of your tank water in this explanation, because it has no bearing on the drop checker value.

However you accomplish the same thing by testing your tank ph with the co2 injected and then letting it off gas and watching to see how much the ph drops. It just takes a lot longer.

As already mentioned, the ph / dkh chart when used with tank water is only accurate if you have nothing else in your tank affecting the waterís ph other than Kh, which is rarely the case. Nitric acid is produced by fish waste, tannic acid is produced by driftwood and can occur naturally in some tap water, those are two examples that render the scale fairly useless because thereís just not much room for any error there.


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But if you already have a lower tank level pH, would it not already off-gas into the drop checker solution as well, regardless of if there is CO2 in the water or not if you have a fairly good gas exchange?

Maybe you can help explain this situation that I had happen:
I get NilocG's 4dkH solution and place it into the drop checker. Solution initially is the standard dark blue color. I place it in the tank, and it turns green, and then proceeds to only fluctuate between green and yellow for the CO2 cycles, never going back to the original blue color. Even when I have CO2 off, and check color in the morning before it comes on the color is green.

My first inclination was that solution was bad, replaced the solution in the checker. Same issue. I then thought that possibly the bottle was bad, got a new 4dkH solution, Ended up with the same problem. Went back and cleaned the drop checker, allowing it to air dry/etc. Same issue.

At this point I started looking more into measuring pH levels to indicate CO2 levels and checked my pH, around 6.8 before the CO2 would come on, and about 6.2 after.

From that situation, it seems to me that even though CO2 levels in the water are minimal when I have a pH of 6.8, there is still a gaseous exchange between the water and the drop checker, causing the drop checker to display the more acidic color.
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post #8 of 8 (permalink) Old 05-20-2020, 08:55 PM
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Co2 adjustment question

Tank ph should have no effect on the ph of the solution because they are not in any contact. The only thing they have in common is that gases from the tank will absorb into the water in the drop checker, and the only gas that should be offgassing from your tank to affect ph is co2. If the drop checker is blue when out of the tank, and green when in, then your tank has higher than atmospheric levels of co2 in it. If it did not, it would stay blue.

So I would say one of two things is happening. Either the drop checker is correct and you just arenít offgassing all the co2 overnight, leaving it at a green color by morning rather than going down to blue, (donít forget fish give off co2 and during the night plants arenít using it) or water is infiltrating your drop checker and contaminating the solution, either by getting into it when it gets installed or evaporating from the tank and dripping down into the solution. What I would try if itís possible, is once your drop checker is green or yellow, take it carefully back out of the tank and see if it turns back to blue. If it does, itís not contaminated, and if it stays green, itís contaminated.


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