Kh and carbonate hardness

[berarma]

Hi.

I was having some BBA that I couldn't get rid of. After increasing micros dosing I saw some improvement on eleocharis but then BBA started expanding. So then I thought it could be a CO2 problem afterall.

I have a cheap PH controller that seems to be doing a good job, calibrated with reference solutions and checked with a JBL test. I've started increasing CO2 and seeing PH decrease to levels that one year ago would have made my fish gasp. So I immediately thought something else should have changed.

I've measured KH of my tap water with a JBL test kit and it reads 6 dKh (maybe a bit less since it shortly changed color for a second after the 5th drop). I think this hasn't changed, or not much, but I remember PH being around 8 and now is 7.2. I regret not having registered tap water parameters over time.

Anyway, now I can lower my tank PH to 6.1 while I used to maintain it at 6.25 because fish would start gasping when under 6.2. And I don't think water is now more oxygenated than it was before. I don't know what exactly has changed and whether this change will last.

If I trust the KH/PH/CO2 table, seeing that my tap water PH is 7.2 and that normal CO2 levels are 2-3ppm, I should have around 1.5 KH. And that would explain that I can get to PH 6.1.

I've read about KH not being the same as carbonate hardness. I'm confused about this comment. It would imply that the KH/PH/CO2 table uses carbonate hardness, not KH.

If I've understood well that carbonate hardness must be lower than KH and it's the former that affects the relationship PH/CO2, then my carbonate hardness could be 1.5 and my KH 6. I wonder where the tap water KH comes from. Phosphates?

Since I'm using a PH regulator to avoid killing my fish, I don't know anymore which target PH is safe to use in the long term. My carbonate hardness could change again and I would only notice because of algae or fish dying. How else could I know when my tap water carbonate hardness changes? I only know about KH tests.

This could be related. My city has a water treatment plant with reversible hydrolysis and it seems carbon filtration has been added lately. Our water sources have high nitrates, fertilizer and pesticidal residues.

UPDATE: KH of my tank water is 7.

 

[Phishless]

What is the KH of your tank water? I did not see that mentioned just that it should/could be 1.5
KH should be a measurement of carbonate and bicarbonate hardness in dKH used in the chart.

 

[berarma]

The KH of my tank water is 7. I forgot to mention.

 

[VaughnH]

You cannot accurately measure the CO2 in your tank water by measuring pH and KH of that water. The equation that relates CO2 ppm to KH and pH is only accurate if nothing else that affects KH or pH except CO2 and bicarbonate/carbonate is in the water. That is only rarely true for aquarium water. You can more accurately measure CO2 by measuring the pH when the water has not had any CO2 added to it for several hours, then measuring it again after the CO2 has been on for a few hours. The ppm of CO2 in the water is 3 times 10 raised to the change in pH power. If the drop in pH is 0.8 you have 3 x 10^0.8, or 20 ppm. If the drop in pH is 1.0, you have 30 ppm. This is based on the belief that the amount of CO2 in water exposed to the atmospheric CO2 is about 3 ppm. Note that this is not 3.0 or 3.00 ppm, so your measurement of CO2 is only good for one significant figure.

 

[berarma]

You cannot accurately measure the CO2 in your tank water by measuring pH and KH of that water. The equation that relates CO2 ppm to KH and pH is only accurate if nothing else that affects KH or pH except CO2 and bicarbonate/carbonate is in the water. That is only rarely true for aquarium water. You can more accurately measure CO2 by measuring the pH when the water has not had any CO2 added to it for several hours, then measuring it again after the CO2 has been on for a few hours. The ppm of CO2 in the water is 3 times 10 raised to the change in pH power. If the drop in pH is 0.8 you have 3 x 10^0.8, or 20 ppm. If the drop in pH is 1.0, you have 30 ppm. This is based on the belief that the amount of CO2 in water exposed to the atmospheric CO2 is about 3 ppm. Note that this is not 3.0 or 3.00 ppm, so your measurement of CO2 is only good for one significant figure.

Yes, yes, I know. What I've tried to do with the CO2 table is similar to what you're telling me here, except that you don't take the tap water PH as a reference but the PH of the tank water after several hours with the CO2 off. Since I'm not adding much to the water that could affect KH I thought that the tap water would be a good reference.

CO2 goes off at 7pm and then goes on again at 9am. I should check the PH at 9am and at 1pm (when the lights go fully on) and use the PH difference to calculate CO2.

Since I'm readjusting CO2 I will wait until tomorrow to check PH again at 9am (the most hours without CO2) and 1pm (lights fully on). And calculate against these figures.

The last time I checked I think I had 6.9 at 9am and slowly raising. Does it matter that it's still raising when CO2 goes on again? I used to think this means there's still residual CO2 from the injection. Maybe I should try stopping CO2 sooner so that it has more time to completely degas and have a better reference for calculation?

Thanks.

 

[berarma]

Tank water PH after 14 hours with CO2 off is 6.98 and increasing very very slowly so I would assume 7. Then my target PH should be 5.9-6 and I should be checking my PH at 9am for significant changes. Right?

Yesterday I managed to get to 6.0 without noticing problems on fish.

 

[VaughnH]

That sounds good to me. I think I would check the pH about an hour after the CO2 comes on. How long it takes to reach equilibrium depends on how big the tank is, how you are diffusing the CO2 into the water, how much water circulation you have in the tank, etc. If everything is working right it shouldn't take much more than an hour to reach equilibrium. And, that gives you enough time to adjust the CO2 bubble rate, let it reach equilibrium again and test again, until you get where you want to be. After you adjust it a few times you shouldn't have to check it again until there is a major change in the tank, like a big water change, heavy plant growth, etc. Of course one unfortunate major change is a big algae attack.

You should be able to use a pH drop of 1.2 (45-50 ppm) without problems with most fish, but not shrimp, if the tank circulation and surface ripple are good.

 

[berarma]

That's what I'm trying to guess now. Ph drops to 6.3 in about 3 hours and it still needs about 4 hours to get to 6. It's a lot.

My tank is 380L (water volume) and I use an Eheim 2078 filter working at full and an Aquamedic 1000 reactor without the bioballs. The water surface is 1.6x0.5m. The reactor is almost full of CO2. It gets the CO2 there but it's very slow.

The theoretical pump flow is 1850l/h and the final water flow of the filter is 700l/h. My reactor isn't probably the best either. I could try the venturi thing on it. I also considered the DIY reactor but never got to finishing it. Maybe I should because buying a good new filter with double the water flow would be very expensive.

I create some surface ripple with the inflow pipe.

Any other ideas about why it might be so slow getting the right CO2 levels?

I'm also worried how would a PH of 5.8-6.0 affect shrimp and snail. Should I definitely raise the KH if I want to maintain both? Right now I have only snails but shrimp are on their way.

 

[berarma]

I have got PH 5.9 and my rainbowfish is having problems to breathe, it's gasping at the surface, and some of the other smaller fish are getting occasionally to the surface too but seem OK. I think I'll stay at PH 6.

 

[Greggz]

If your KH truly is 7, then your FULLY degassed pH is probably closer to 7.6 to 7.8.

i would try leaving a cup full of water out for three or four days and be sure it completely degasses. You might see a different reading than you are getting now.

I know in my case my tank water does not degas fully overnight, even with heavy surface agitation and a bubbler.

My fully degassed pH is 7.3, right before CO2 turns on in morning it's about 6.9, and I drive it down to 5.95,

Any lower and my Bows show some stress. Bows are sensitive to oxygen levels, so you might also consider creating even more surface agitation for theim.

 

[berarma]

If your KH truly is 7, then your FULLY degassed pH is probably closer to 7.6 to 7.8.

We must trust my JBL testing kit. Since I've read that KH isn't all carbonate hardness, and that the KH/pH/CO2 table is only accurate when KH is from carbonates alone, I guessed my KH is mostly from non carbonated sources. I get to this conclusion after reading this post by Tom Barr: https://barrreport.com/threads/co2-ph-kh-table.10717/

Please, correct me if I'm misunderstanding.

i would try leaving a cup full of water out for three or four days and be sure it completely degasses. You might see a different reading than you are getting now.

I know in my case my tank water does not degas fully overnight, even with heavy surface agitation and a bubbler.

My fully degassed pH is 7.3, right before CO2 turns on in morning it's about 6.9, and I drive it down to 6.95,

Any lower and my Bows show some stress. Bows are sensitive to oxygen levels, so you might also consider creating even more surface agitation for theim.

I'm trying this right now. Your numbers are very similar to mine. I just lack the fully degassed pH reading that I don't think won't be too different to yours. We'll see.

Thanks for all your ideas.

 

[berarma]

I've had a glass of tank water degassing for 36 hours and the pH is 7.6 measured with the electronic controller and with the JBL drop test 6.0-7.6 (the color is the more intense blue in the scale or even a bit more).

Taking this measurement as valid I should drop the pH to 6.4 to have around 40ppm CO2. But this would also mean I've got CO2 concentrations up to 120ppm at pH 6.0 without problems on fish.

I don't know what this means. I think I should redo some of the tests double-checking everything. Still, I think there's little margin of error in this last measurement.

 

[Greggz]

Your pH and your KH make more sense at those levels. I didn't think your pH was really 7.0. As to how far to drop the pH, well that is always up to debate.

I think you will find many here dropping it by 1.4 or so. Also be sure to calibrate your pH controller on a regular basis, then throw out the drop tests.

As to some of it not making sense, well this is a rudimentary methodology that we use. Other factors could be in play. For me, when I get much past a 1.4 pH drop, my Bows start going to the surface and showing some stress. But that doesn't mean it will be the same in your tank.

In the end, it's the plants and fish that should drive your levels. Once you figure that out, the pH controller can help you keep the numbers at good relative values.

Good luck, and I hope you get it all worked out.

 

[tiger15]

Please explain what is non-carbonate KH and the sources of non-carbonate hardness.

I know in my case my tank water does not degas fully overnight, even with heavy surface agitation and a bubbler.

My fully degassed pH is 7.3, right before CO2 turns on in morning it's about 6.9, and I drive it down to 5.95,

Your tank water will never be fully degased overnight, because your fish and plants are generating, not consuming CO2 off photo period, right?

 

[Allwissend]

Please explain what is non-carbonate KH and the sources of non-carbonate hardness.



Your tank water will never be fully degased overnight, because your fish and plants are generating, not consuming CO2 off photo period, right?

Don't quote me on this, I'll have to refresh my memory over the weekend. From what I remember the KH tests we use actually measure alkalinity (as in ability to resist Acids). As such things like PO4 also play a role but the majority of the ions that influence the result are normally HCO3 and CO3. The kits are calibrated to report the values as CaCO3 equivalents (or derivatives dGH). This does not mean they actually measure only the Ca or the CO3 levels.

The conclusion, like all hobby test kits you get an approximation with a wide confidence interval.

I agree with you, water will not degas (as in come at equilibrium with the atmosphere) overnight. I think it is a question of volume, turn rate, surface area and additional production. If you aim a 1-1.4 drop based on the morning pH you will aim always lower.

Best approach is to keep/wash an airstone in rodi water, dry out and put it in a small volume (100-500ml) of aquarium water. With a pH meter monitor the pH change. When it stabilizes (within 24h) that is your degased pH. Also know that this pH value can change... Overnight... Depending on what is released in the water.

 

[tiger15]

Not only that overnight water will not degas all co2, fish, micros and plants will add co2 to water by respiration during non photo period. In NPT, splitting the photo period to allow a siesta period to recover co2 is recommended.