Backyard Aquaponics
A place to discuss aquaponics

Hello!

My system is 3 weeks old. It's a small system aprox. 100 lt, tank fish (Koi) and the same size for growing bed (8 inches gravel) with tomato plants. My pH is 8.0 to 8.2 and the amonia, nitrites and nitrates levels are safe. The fishes are healthy but the new leaves of my tomatoes were light green few days ago and starting to die today.

Any Help?

Andy (Puerto Rico)

Your pH is too high and locking out nutrient uptake.

System is only 3 weeks old. Have you seen ammonia and nitrite spikes from cycling? Do you have any Nitrate?

I would tend to agree that your pH is too high but for a system that has not yet cycled, that is not uncommon. However, I can't quite tell but what kind of gravel are you using? If that gravel is marble or limestone, you may find it nearly impossible to ever bring you pH down far enough to have very happy plants.

First order of business will be ascertaining if your system has cycled (it often takes 6 weeks or more to fully cycle a new system using fish.) And then we need to know if your gravel is going to continue buffering your system over 8 long term.

Nitrate deficiency in plants usually shows up as lower/older leaves yellowing first. If this is your problem, I suspect that you just have not cycled yet and there is little/no nitrate for your plants.

Iron deficiency usually shows up as new leaves yellowing with the veins remaining green at least at first. This can be a combination problem between lack of iron in the water and too high a pH. Adding chleated iron will help but with the high pH it will still be minimally available to plants.

Seasol or maxicrop added to the system in small amounts can help plants out with potassium and micro-nutrient deficiencies until your system matures a bit.

What can I do to lower mu pH? feed more, add more fish?

I think my gravel is limestone, I try to change but right now I can't found lava gravel in Puerto Rico. The green light leaves are the young ones, the older are ppretty much normal.

You will probably want to switch your gravel to either, river rock (most quartz so it doesn't affect pH), lava rock, granite, expanded clay (found in hydroponics shops). Other options that people have experimented with include....
Sand
coco coir
maidenwell
sea shells

Sand tends to say pretty moist as would coco coir. Maidenwell actually tends to drop the pH quite a lot and could have some negative minerals for the fish. I have lots of sea shells in my AP system. The sea shells work as media and they tend to buffer the system to 7.6 which is better than 8-8.2

I do not advise trying to lower you pH as long as you have limestone as your gravel. The trouble with the limestone is it will buffer to a particular pH and whenever you add enough acid to change your pH, it will dissolve enough limestone to bring the pH back up to the buffer level. Adding more acid to bring the pH down will only result in bouncing the pH which is even worse for the fish and plants.

In the mean time while you try to find a better media for your grow bed, it sounds like you might want to provide some iron to those tomato plants. Chleated iron is the best choice for adding a small amount to the system but if you can't find that, iron sulfate might help in a pinch. It would probably be best to dilute according to the directions and spray on the plants as a foliar feed. Carefull, it does tend to stain.

I had a retailer garden few years ago and I work with coco coir, it's excellent growing media and have antifungal properties but I have my reserves with AP bacause retain a lot of water and humidity. With a system drain and flood I think that aeration problems can occur.

Can I make some tets to the gravel before to check their properties?

To test the gravel you might get some distilled water and soak some gravel in it for several days and then check the pH of the water. If the pH goes up close to 8 then you have your answer about the gravel.

Or you might even use tap water to test it but that will only work if you tap water (after being bubbled for a while) tests close to 7. Since most tap water might test around 7 out of the tap but after outgassing the CO2 is actually closer to 8 it wouldn't help to test with it.

hello, Im from Puerto Rico, Camuy... you can get it at Empresas San Pablo en Lares.....