Can CO2 cause KH to increase in tank?

[bjorn]

I'm a bit confused! I've been trying to find a good dosage for CO2 that suits my tank and water. Each time I measure the values seem to fluctuate a lot and never quite hit what I want. I'd like to have a good level that helps the plants but also reduces my PH close to 7.

I finally managed to get around PH7, but the values are confusing. I used test kits on my tank and on some tap water I've had standing for 36 hours to compare it with and found that the KH in my tank increased compared to the tap water.

Isn't KH supposed to be a constant that doesn't change depending on the amount of CO2 I inject?

Tank: 80L
CO2: Pressurized tank + ADA Diffuser (during day time only).

Tap Water
PH: 7.6-7.8+
KH: 12

Tank Water
PH: 7.0-7.2
KH: 13-14

The problem is also that if I use a PH/KH chart for my tank water it seems I'm using too much CO2, but if I reduce it my PH will go up instead.. so what do I do?

I also have a drop checker which shows lime-green.

I'm also a bit worried about my fish and wondering if something I've done with Co2 has made them ill.. The fish has become less active and keep themselves towards the bottom of the tank and not moving about very much.

Any advice?

 

[Garuf]

I wouldn't trust the test kits, your description of fish activity sounds like you've reached your co2 limit.
The only reason I can imagine that co2 would change the actual KH is if there's rocks in the tank which are being dissolved by the co2, landscape rock has this tendency.

 

[bjorn]

Oh really? I do have some stones from the local fish shop, but they might be for outdoor ponds rather than tanks, can't identify what it is either. Might remove some of those and see.

But with the fish, I thought sign of too much CO2 they would go to the top of the tank and not bottom. They are no better today, they seem to actively stay away from the surface and remain towards the bottom of the tank. Even at feeding time when they normally go up and grab whatever is available.

So you recon that means too much CO2?

 

[dw1305]

Hi all,
Fish can be actively stressed by high CO2 levels long before they start gasping at the top of the tank. The listlessness you describe is caused by the "Bohr effect", this is that "an increasing concentration of protons (H+) and/or carbon dioxide will reduce the oxygen affinity of haemoglobin".

So insufficient oxygen in the blood leads to stressed fish with little appetite and sluggish movement. Therefore you need to turn the CO2 down immediately and/or add more oxygen. It may be possible to run the CO2 at the level you now have if you can add oxygen efficiently. Tom Barr may be able to comment when he is on forum next, but I believe he has started using trickle filters specifically to up the O2 content of his tanks.

My personal choice is not to use CO2 for this reason.

cheers Darrel

 

[a1Matt]

Just one thing to add...

One way of immediately getting the co2 down is by a large water change.

 

[bjorn]

Thanks for the advice!

I did a 60% water change and reduced the CO2. After 24 hours the fish seem much happier.

I also removed the stone I had in the tank, 3 large pieces. Since then the KH level has remained the same as the water I put in. Previously KH increased by 1 or 2 degrees.

Levels of PH/KH has been stable at the same values now for 2-3 days:

PH 7.2
KH12

Drop Checker shows Green.

Does those type of values sound about right both for fish and plants? I guess that works out at roughly 22ppm.. I know the aim is 30ppm but don't want to stress the fish again with changing levels.