Backyard Aquaponics
A place to discuss aquaponics

Hi
Our system has been up and running for about 4 weeks now (with fish); 7 in total. pH still remains high around 8.0-8.2 despite the system having cycled and ammonia and nitrite at 0, nitrate about 10. Tomatoes are showing strong incurling of the leaves and lower leaves are withering. I am assuming there is nutrient lock-out problem happening. The water we are topping up with is around 7.2-7.4. Therefore, I would suggest the place where the high pH is originating is in the expanded clay we are using. There is algae on the sides and bottom of the tank, but none in the water.

1) Does any one have direct experience with using peat to lower pH. Local aquarium stockist suggested it as a good natural way to lower peat gradually and help keep the water clear (not that that is a problem).
2) Is it just because we have a new system - I have had commented that the pH will go down in time - just not sure how long "in time" should be.

Thanks!

Regular expanded clay should not be causing your high pH. Let me ask you something about how you tested the water your are topping up with. Is it tap water and did you test it right after drawing it from the tap or hose? If you tested it fresh from the source, that pH of 7.2-7.4 is probably a false reading. Take some of that water and stick an air bubbler in it over night and test the pH again. If I pH test my tap water (well water) right away, it will test with a pH close to 7. If I let the CO2 out gas and test the pH again, I will get a truer reading of 8. Water right from the tap usually has CO2 dissolved in it which acts as an acid but once it is flowing through an AP system and the CO2 escapes, the true pH of that water shows up.
When you say the system has cycled, did you see actual ammonia and nitrite spikes? 4 weeks is a pretty short time for cycling with fish. It took about 3 weeks for my fishless cycled system to take the sudden pH dive.


1) I don't have experience using peat to lower pH. My experience is if your media is what is raising your pH (buffering) adding acidic things won't really help it balance. I expect that peat will turn you water a tea color.
2) I suspect that it is because of the new system. pH does go down in time unless you used limestone or marble or shells as your media. For cycling with fish, I would guess the pH should drop somewhere between 4 and 8 weeks into cycling depending on temperature and feed rates. My pH didn't drop until about the time my nasty high nitrite spike was starting to drop.

Once you do the little test on your source water (if it is in deed tap water) then we should know more about what exactly your trouble is. In the mean time, add some chleated iron and seasol or maxicrop into your system to help those tomatoes.

TCLynx

Thanks so much for your very helpful response. Ok, so here are the results of the outgassing experiment:

1) I pulled a bucket of water out of our "topping up" tank (garbage bin that sits there for about a week before it goes in to the pond - has a lid on it, gets treated for chlorine), put an airstone in it over night and took the reading tonight: 7.4
2) Took a sample from the fish tank - 8.0.

In answer to your question, yes the system has definitely cycled. Went through ammonia spike and nitrite spike (the nitrite spike lasted a good week or so) and now both sit at zero. Nitrates at about 10.

With regard to explanded clay, I did an experiment on it early on in the piece and ground up the gravel rocks, then did a soil pH test on it. It was off the scale alkaline. Don't know how scientific that was, but there you go.

Any further thoughts.

Many thanks again.

Got me confused.... you say you "ground up the gravel rocks"... and tested them...

Expanded clay... is just that... expanded clay.... not a gravel rock... and expanded clay is pH neutral....

Unless you're buying some dodgy product that's been labelled andor flooged as "expanded clay"????

Very interesting. Did you rinse the expanded clay before starting up the system? Very odd that. I've never used the stuff but I've never heard anyone mention it having any effect on pH. Is there any other material in your system like concrete? Say a tank made of concrete or a concrete block as a hide for the fish? Did you add any sort of buffering material early on for the fish?

I wonder if there is anyone out there with this sort of experience using expanded clay. I'm kinda at a loss. I really doubt the expanded clay should have much buffering capacity but something is definitely causing your pH to be high.

Hum. Do you have an algae problem? What time of day do you usually test the water? If the pH is high late in the daylight hours and there is an algae problem then try getting up before dawn and checking the pH to see if it is really low then.

Otherwise, I don't know. Perhaps try the peat and see if it has an effect.

Hi TCLynx & Rupert

Will answer questions that you posed:
1) Yes, washed the expanded clay before it went in quite thoroughly.
2) No other material in the system, apart from the pump and airstones (and a little bit of PVC pipe for the fish to hide in)
3) Usually test around 6.00pm. So will try an early morning test.
4) No algae problem in the water, although algae on the bottom and sides of tank.
5) By "gravel rocks" I mean expanded clay pebbles - sorry for the confusion in terminology. They are genuine expanded clay pebbles.
6) Added salt at the beginning when fish went in and have been using Seasol foliage spray in the past week and one small addition to the water of Seasol a few weeks back.
7) Yes, the test on the crushed expanded clay was interesting - I was expecting a neutral result, but was amazed to see a deep, deep purple. Again, not sure if that's how you test it, but it seemed logical to me.

Will be interesting if anyone else comes up with something. Might just be a case of being patient not my greatest virtue.

I've tried adding peat to water in the past- it takes a long time to act. In an aquarium it's viable to add it due to the low volume of water in your average aquarium and therefore, lower quantity of carbonates, which usually 'cause' the alkalinity.

If there's any carbonate in the clay balls it will fizz if you add a drop of acid, but I think whilst there are a few producers, they shouldn't have anything that will affect the pH too much.

As mentioned, if there's any algae the pH can go up with only a small concentration. Other than that, selective uptake by plants of major nutrients (mainly N and K) will alter pH.

what brand of expanded clay are you using?

Expanded clay we are using is Canna Aqua Clay Pebbles.

Early morning pH reading from fish tank 8.0. Reading this evening 8.0. Very stubborn.

Thought clay was ph neutral. Wonder if they ever get a bad batch. Nothing else in the system.

It's weird that your water is 7.6, but with "neutral" media in it, it's 8.0. I suppose you could do an experiment with different amounts of media, and test them all over time. So 1 jar would be just water, 1 jar would be 75/25 water/media, 1 jar would be 50/50, etc.

If it really is your media, you're going to have lots of problems at 8.0 and nutrient lock out.

When you tested the clay.... crushed it into water... did you use your tank water??

If you did... then your tank water pH is 8.0.... the clay is neutral...

When I tested the clay, I simply crushed the pebbles down into a sand-like composition. I then ran a SOIL pH test on them - I didn't use any water. As I said, I don't know how good that was as a test - but it seemed logical???

Sooo.... are you testing your water pH with the same "soil tester"???

I've got a half a bag of Canna...

Tomorrow I'll run three tests using the API test kits that most of us use...

(1) pH of water

(2) pH with whole balls in the water

(3) ph with "crushed" balls in the water...