What causes KH in tank to be less than KH of source water?

[Lev]

Question: what causes your aquarium KH to be Les than you tap water? My tap waters 5dh, display tank (planted sand and gravel) is 8dh, but nano tank is <1dh.

Background: This is regarding My 20L nano aquarium with some nano fish and shrimp in. Aqadvisor says the stocking and filtration are good for adult specimens of the numbers I have.

I do 50% water changes 1-2x weekly. The tank was fishless cycled and set up with stock in for 1 month. Not had ammonia or nitrites at all since adding shrimp and fish, nitrates usually 5 before water change (10 if I've been overfeeding).

Tank is planted, low light. Dosed with recommended doses ferts inc carbon source but not gassed substrate is one designed for planted tanks.

THE PROBLEM

after a fish death I rechecked a night time pH and it dropped at night when plants respiring to 5.5!!!!! (Normally 6.5) this returns to normal during the morning when lights on.

Finished work late so LFS is closed but I was wondering if any household products suitable to raise KH? Also what causes it to drop? Its measuring calcium carbonate right - does someyhibg bind to it ? :-\

 

[TMaier]

I added oyster shell to my canister to stabilize the KH.

 

[PerfectDepth]

What is your substrate? If it's ADA Aquasoil or a similar type then it could be the reason your KH is dropping. It is acidic and uses up the KH. Your tap water KH is sufficient to replenish it, so I recommend just doing water changes more frequently until it becomes more stable. Even KH of just 1 degree should be a sufficient buffer to keep your pH right at 6.9 or 7.0. Good luck!

 

[Lev]

I added oyster shell to my canister to stabilize the KH.

This is sponge filtered. Is there any harm in adding whole shell into the tank itself (not sharp)?

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[Lev]

What is your substrate? If it's ADA Aquasoil or a similar type then it could be the reason your KH is dropping. It is acidic and uses up the KH. Your tap water KH is sufficient to replenish it, so I recommend just doing water changes more frequently until it becomes more stable. Even KH of just 1 degree should be a sufficient buffer to keep your pH above 7. Good luck!

Ahhh good point - I can't remember the brand name but it did say "maintains an acidic pH around 6.5" in the info. I want the pH to sit at 6.5 which is optimal for the little guys but having no buffer and dropping by 1 overnight is scary [emoji28]

I'll change the water daily for a while...its not like doing 10L water changes is difficult and see if the problem settles



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[PerfectDepth]

Ahhh good point - I can't remember the brand name but it did say "maintains an acidic pH around 6.5" in the info. I want the pH to sit at 6.5 which is optimal for the little guys but having no buffer and dropping by 1 overnight is scary [emoji28]

I'll change the water daily for a while...its not like doing 10L water changes is difficult and see if the problem settles



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Actually, the pH dropping only temporarily overnight is not a concern for the fish, and it's actually great for the plants, since it only means co2 concentration is building up overnight, thus more co2 is available for the plants to use when the lights first come on. This is not the same as a pH "crash", which happens when KH is depleted to almost zero. As long as pH is returning to the baseline during the day everything will be fine. It's your KH you would want to keep an eye on and make sure it does not get totally depleted, causing a true pH crash.

 

[Lev]

Oh ok thanks! my KH when I tested it pre water change just now is <1dh ... After water change is 3dh

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