Help! Aquaponics Garden pH Too High - Need Advice!

[mcstatz5829]

TL;DR Summary

Could increase from 0 to 4ppm ammonia increase pH from 7.4 to 8.2?

Hi everyone, hoping for some quick help.

I’m trying to get the chemistry right for an aquaponics garden I’m building. I screwed up pretty bad the first time and just swapped out almost 100% of the water (there was a residual 2-3 gallons in the bottom of the growbed).

Last night added in about 60 gallons of filtered drinking water. Tested the pH at 7.4. When I tested the pH, I don’t think there was enough time for the 2-3 gallons in the growbed to fully mix in.

Last thing before bed was adding some urea to decompose into ammonia.

This morning pH was 8.2! And ppm ammonia was 4.

What I don’t know:
Buffer of the water (suspecting weak)
pH of the residual water (prior tests were 7.2-7.4, but I believe the water was brackish and the tests inaccurate. Freshwater aquarium testing kit used).
Prior ppm ammonia (assumed 0, water was straight from tap filter)

I’ve read urine tends to be acidic, but I’m guessing that changes as the urea decomposes into ammonia?

What I’m trying to hopefully understand is if the majority of that 8.2 pH is because of the ammonia, which would be good, or if pH will stay elevated when the ammonia is converted to nitrites, which would be bad.

 

[Borek]

This is tricky, for many reasons. The simplest approach says that 4 ppm ammonia means around 2×10^-4 M*, assuming nothing else is present such a solution would have pH of around 9.7. Any buffers present will make the change lower, but at least there is no doubt ammonia can't be ruled out as a reason behind the pH change.

* I believe kits check the presence of ammonia and ignore ammonium ion, so the total concentration of both forms would be around ten times higher.

 

[mcstatz5829]

Thanks! That's exactly what I needed to know.

I did some googling over lunch and was able to convert to molarity (assuming pure ammonia solution) and came up with something similar. Been over 10 years since I've been in a chemistry course.

Interesting if the test kits only include NH3 and not NH4+. Maybe only the NH3 is toxic to fish?

 

[Borek]

Partially that, but making a test that will react with both can be challenging. Once you know pH and concentration of either ammonia or ammonium ion (doesn't matter which one), calculating the other is trivial.

 

[mcstatz5829]

Do you know if water conditioner can throw off the tests?

I'm in Indiana with very hard water and my city uses chloramine. First go at this, I filled up from the tap and used a water conditioner designed to remove the chloramine/chlorine.

I then used the tank to urinate in for a week straight. Ammonia levels didn't budge. I added 10% ammonium hydroxide, and ammonia levels barely budget even after a full gallon in a 150 gallon tank. The greenhouse stank of ammonia but it only got to 4 ppm.Fast forward to round two. I used a drinking water filter that removes chloramine. Had to lug 5 gallon buckets to the greenhouse and back and only got it halfway filled right now after 3 hours yesterday. Urinated in it twice, and already I have ammonia levels high off the scale (8+ ppm)

Good news is the tank is only half full, so I can dilute it down (3 more hours of lugging water...)