Why does the PH go down?

[Tina Cresswell]

Hi the PH in the Fish Tank dropped suddenly to 4.5. The temperature in the poly tunnel has suddenly gone up to a max of 28 c, and I removed one grow bed that had been covering the tank. Could it be as simple as more light and more heat? I have increased oxygen to try and counter it, and the surface has gone up to 7, but at the bottom it is still 4.5, so I think it is improving.

[matthew ferrell]

What do you have in the tank fish wise, and how much?  What was the pH before? Have you buffered your water?

[TCLynx]

pH falls naturally as a byproduct of the bio-filter operation.  As the bacteria convert ammonia to nitrite and nitrite to nitrate they use up alkalinity and the pH drops.  You will probably want to buffer the pH up a little bit to keep it from dropping too low too fast.  something like potassium bicarbonate alternating with calcium carbonate to keep a stable pH range works well.

Now I'm not sure why the pH near the surface would be different from the pH down at the bottom unless you have an algae problem and really poor circulation/aeration.

An increase in temperature along with increased feeding would also increase the load on the bio-filter and can cause the sudden drop in pH.

What does your ammonia test say now after the sudden pH drop?  Has your ammonia spiked up along with the sudden pH drop?

[Tina Cresswell]

Thanks for all your help! I am just starting up the system, so have recycled the old pond water mixed with some fresh, and there are only some minnows and a solitary goldfish at the moment in about 500 litres (its not full yet) I am not feeding yet as I think there is enough micro life in there. The water is in the tank in poly tunnel now, and so is getting much warmer. First few days the PH was 6.5 then I took off one grow bed exposing the tank to a third more light, and at the same time it got really warm. I have a digital ph monitor so have not measured the  ammonia levels, but I am able to measure at different depths. This morning it is back up to 6.5. Have put a better pond pump in yesterday, and replaced the grow bed, so I think I have turned it round. Getting 50 organic carp first week in April, so want to be sure its steady. Thanks again!

[TCLynx]

Protect the pond from excess light and make sure you have plenty of filtration and aeration and you should be fine.

500 liters sounds way small for 50 carp though.

[Tina Cresswell]

Going to fill up later, it takes 1300 litres when full so should be ok, thanks for your help!

TCLynx said:

Protect the pond from excess light and make sure you have plenty of filtration and aeration and you should be fine.

500 liters sounds way small for 50 carp though.