Aquaponic Gardening

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Hello All,

Every expert started as a beginner, so here I go....

I am helping to start a new AP system at a high school in southwestern Ohio. My sweetheart is a science teacher. She intends to use the system as a "living lab". I was there yesterday, watching the kids test for pH. One said, "I feel like a scientist!".

I like it when my sweetie smiles. 

ph brings me to the point. We are getting a consistent reading of 6.0 , lost our bacteria, and are open to all suggestions from the veterans on this forum.  Here are the system specifics:

250 gallon fish tank

130 gallon sump

2 grow beds 41 x 41 (it's a standard aquabundance system)

We have been cycling for almost a month; here are the readings today...

6.0 ph

ammonia between 4-8 ppm

nitrites 0

nitrates 0

The top off water reads a pH of 7.6 , and decent kH (40 ppm, although off a test strip-- we need to spring for a complete API kit). We have about a 10 kh reading for the tank, and it is not budging.

We had an ammonia spike yesterday of 8, I replaced 20 gallons of water, and the reading an hour later for the tank was 6.4 . Today it's back to 6.

Should we keep replacing the water?

We have been adding about an eighth cup of potassium and calcium carbonate daily, with no change. Then  they seemed to be falling out of solution, so we stopped adding them a couple of days ago.

We also put a couple of pounds of crushed oyster shells in last week, which helped for a couple of days (reading 6.4) and then back to 6.

We have no plants or fish in the system. I am a complete n00b at this. Shan has a great grasp of water chemistry, I am just attempting to do some legwork for her.

Any insights or suggestions (or questions I should be asking) would be greatly appreciated!


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Yeah, keep replacing the water and get your ammonia down to 2-4ppm.

If you're trying to adjust and stabilize your pH, it's better to use potassium and calcium bicarbonates, rather than plain carbonates. Bicarbonates are what increase your water's buffer.

Thanks for that advice, Alex. I'm going to switch out about 50 gallons tomorrow or Friday. I had been reading the forum for a couple of weeks before I joined, and saw where to get potassium bicarb for a reasonable price at . I haven't seen any place to buy calcium bicarb; is it ok to alternate the K bicarb with Ca carb?

Sure. Just keep in mind that calcium carbonate isn't going to provide a noticeable buffer, just raise your pH and supplement calcium.

Excellent, thanks again Alex. I am learning something every time I log into this forum; you guys rock ! 

Lol, I know the feeling. Happy to help :)

Hi Alex. This post said no plants or fish so why would you change out your water at this time? I understand the adding of potassium bicarbonate to help stabilize the PH. I must be missing the picture here. Can you please explain.

Certainly. If your ammonia level is above 4ppm, it can actually hinder the reproduction of your nitrifying bacteria. More ideal parameters are around 2-4ppm.

Thank you Alex. This site is awesome... I learn more and more every day.

Alex - Calcium BiCarbonate does not exist as a solid compound, so we have to supplement with calcium carbonate. The CO2 in the water reacts with the Calcium Carbonate and converts it to Calcium Bicarbonate.

Good catch Scott. Typo on my part :/

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