Backyard Aquaponics
A place to discuss aquaponics

Alright Thank you Sleepe

I am having the same problem right now. I have a FT which holds 40 gallons of water and feeds two grow beds. I have 12 tilapia (15-25g fish) in the system now. The pH is really high right now, at 8.0, which is causing my plants to suffer but the fish seem fine. I was going to salt my system today, could anyone verify my numbers? 40 gallons = approx 150 L, using the 1ppt that is 150 grams of sea salt... Seems like alot! The nitrites have sitting around 4.0 for about 10 days now. They climbed up there after a water change, but have been dropping VERY slow.

I plan to get some muriatic acid to add to the system tomorrow, unless there are other recommendations. I feel the 8.0 pH is inhibiting the nitrite to nitrate converting bacteria.

I would suggest you leave the ph where it is most plants may prefer 6.5 but bacteria around 7.5.Adding hydrochloric acid is likely to crash your biofilter when you need it the most.
1 ppt is the recommended dose for preventing fish suffering the effects of nitrite.

Edit and again try to up the DO levels.

Sleepe - Thanks for the insight. The pH is at 8.0 so it's even high for the bacteria. My plants haven't grown an inch and are dropping fruiting flowers left and right, because they don't have enough nutrition to grow them. I will add salt to the system today. As for DO, I have a air pump with two stones in the system, so I'm sure DO is as high as it can go.

Your nitrate colony is coming on strong but it is still establishing is why you are seeing nitrites dragging their feet in coming back down as the conversion continues.

It will be some time till you see good plant growth but you could lower your PH slowly to assist and add a seaweed extract to help also.

Salt as recommended.

p.s. you doing well, all looks good.

If you decide to use hydrochloric acid, add it in very small doses with 24 hrs between doses. I have a 55 gal FT and 30 gal ST and when I used HCl, I only added 1-2mL at a time to the ST. I once added 2mL 8 hours after adding 2mL because the pH didn't change that much in that time, but the next day the fish were not happy. Give your system time to fully settle before you make any adjustments. (I used Muriatic Acid from a pool supply, FYI.)

EDIT: High pH is good for bacteria colonization, but might effect nutrient uptake. Unless your system somehow raises higher than pH 8.0, let it do its thing.

Thanks for the advice guys.

I called around pool supply stores, but they only sell 2 gallons of HCl. Don't need all that extra acid! I meant to ask the neighbors pool guy when he was there yesterday, just never made it out to ask him.

There are plenty of systems that run at Ph of 8 for many years. Mine was up around there for a long time. The nitrification process itself is acidifying.

If you cant help but fiddle then do not add the acid to your water directly, instead pull some of your water out, treat it to an acceptable level and the add it back into your system. Much safer for your fish that way.

Also when adding salt, make sure it is pool salt. You dont want to add any salt that has has anti-caking agents.

Yep... treat your top up water... not your tank water....

Treating your tank.. with fish in it... is fraught with danger.... and a waste of time... if you then top up with high carbonate source water anyway...

Treat the problem... not the symptom... it will take time... but eventually, with nitrification.... pH will exhaust the carbonate hardness... and fall..