Backyard Aquaponics
A place to discuss aquaponics

I thought I remember reading (here?) that adding limestone to your system will keep the pH at 7.6 because limestone stops dissolving at 7.6 pH... so as soon as your system drops below 7.6 some of the limestone dissolves to boost it back up to 7.6... but I've also been reading that adding limestone to aquariums is bad and someone also mentioned in a post here that supposidly all the literature says not to add limestone... oh, woooe woooe is me.

what is your pH?

I thought that was crushed shells?

well my pH s above 7.6... probably 8.5 or something because I just filled up the 300 gallon tub with city water (which has high pH 8.5-9.0) and threw the de-chloramine-ator in it (I would have prefered to wait out the chlorine instead of using chems, but from what I've heard it takes a long time (42 days) for chloramine to disappear).

The limestone question doesn't necessarly apply to me right now, was just wondering about the future and figured if it stops dissolving at 7.6 pH I could just throw a few chunks in there now to give my crawfish a place to hide and for any future pH problems.

Also, the river that I got my sunfish from has a lot of limestone in it naturally... I wasn't smart enought to test the water when I was there but will next time I go down there. Figured the pH must have been high due to all the limestone (central texas, we live on top of limestone).

Dan,
From what I've been reading now, some people use shells, corral or limestone. But I've also read don't use limestone because it will make your pH to high... but maybe that's for certain types of fish?
Also is that carrot in your picture from your aquaponics system? Lot of tiny roots like I'd expect with so much water, but doesn't look like it cracked/split like they say carrots will do with to much water. I just planted some carrots in my system to see how they'd do.

It, and 864 other carrots were grown in my hydroponic system (pea gravel). I did not have a problem with splitting, unless the top got uncovered and dried out. If they stand in water they can split open too. My cycle time was 4 hours apart with a slow 30 min drain down time.

mrgrace limestone is basically Calcium Carbonate, like all carbonates it's an "alkaline" compound .

As such, like coral or crushed shells, it's often used to buffer the acidic tendancy of an AP system.... ie to pull pH 6.5 > pH 7.5.....

I'm not sure that it stops dissolving around pH 7.6, it may well do. I seem to recall something similar myself. But it does so and needs an acidic solution to dissolve ie pH 6.0 > pH 7.6.....

You have the opposite environment... an alkaline pH (pH 7.0 > pH 10.0)

At your pH levels, especially after water top-ups you certainly don't need any more buffering in that direction... if anything you should probably be buffering the other way pH 8.5 - 9.0 is extreme.

Let the system run for a while and see where the pH trends too.... if it continues past ph 7.5 it will probably take a while to get anywhere near pH 6.0 which is the other end of the extremes.

I went and caught some more bluegill for my system, I took my test kit with me today and tested the water in the river.

ph 8.5-9.0 (same as my tap water.. no suprise as this is where my tap water comes from)

oxygen was 6 mg/L

barely a trace of ammonia in the water
no detectable nitrite
barely a trace of nitrate in the water

I guess it's about what I expected. I guess my 8.5-9.0 (hard to read my chart at this level) pH is about right for my fish then... since it's where they come from.

Awe nuts, I just realized I should have tested water hardness and calcium content when I was there... I've already got the numbers for the water from my tap.. I think they should match up pretty closely as well.

You fish might be doing fine, as indeed it appears they are matched to their natural water parameters but you may have a problem with your plant growth at those pH levels....

Those pH levels will lock out many of the essential trace element minerals from your plant uptake....

Suggest you research if your sunfish can tolerate pH levels closer to at least pH 7.0.... if so then you can raise your pH to this level and your plants will benefit greatly

You certainly don't need and shouldn't add any limestone, shells or coral.

Most any of our native fish should be able to take a neutral pH.

bluegill should be able to handle just about anything I think... they're everywhere in north america (and apparently in japan they're invasive). I totally didn't think about the pH messing with the plants nutrients (duh). I had a smaller setup going with a 50 gallon barrel and my water went to 7.0-7.5 by itself. I'll hold off on adding any limestone unless it's warranted.

I might test my soil in the garden and see what the pH of it is... I mean, it's limestone everywhere in central texas hehe. Some of my plants seem to have nutrient deficiencies at times and now I wonder if it's the soil pH.

keep in mind that;

ammonia is more toxic at elevated pH
bacteria should colonise quicker at 7.5 -8.5
nitrification will lower ph