Backyard Aquaponics
A place to discuss aquaponics

I'm a newbie (obviously). I got my first, indoor system up and running in March. My fish are thriving. Some of my plants wilted in the hot and humid southern USA summer, but most of my plants grow to be big, luscious, and leafy green. But nothing will flower. Below are some of the specifics of my system. I suspect it is either a pH problem or lack of nutrients, but I'd very much appreciate any ideas on what could be wrong. I sent a sample off for water testing last week to determine if there is something lacking from the water. Also, if anyone can tell me the concentrations of nutrients/minerals needed (not just a necessary list), I would appreciate that also.

Thank you.

Volume: +/- 220 gal fish tank @ 1:1 ratio
Fish: 25 total catfish/koi (4-6")
Plants: tomatoes, spinach, strawberries, peppers
Light: +/- 3000 lumens/sqft
pH: 6.4
nitrogen: 0 ammonia, <0.25 Nitrite, 20-40 nitrates

Your pH is low. You may want to double check it. Any lower and your bacteria colony is likely to crash which will lead to ammonia and nitrite spikes.

What are you feeding your fish?

Have you tried adding seasol/maxicrop?

With the majority of the plants in your system being fruiting plants and having high nutrient requirements I'd say you probably have a lack of Potassium in the system, and/or Magnesium, but more than likely Potassium IMO.

Do you have any pics of the plants?... they help immensely when trying to diagnose a deficiency. What do the leaves on your plants look like?... especially the older lower leaves, are they pale or yellowing?... maybe browning off around the edges?

Try adding a slightly heaped teaspoon of Potassium bicarbonate (sold in Aust as Eco-Fungicide, should be available in the US in some form) per 1000L of system water, this will add Potassium and also buffer your pH up slightly.

Then add some Maxicrop with Iron as Arbe has suggested. You could also add a teaspoon of Epsom salts per 1000L, just to cover the possibility it's a Magnesium deficiency, this is a shotgun approach, but if you want to try and determine which nutrient is deficient then I'd try the Potassium bicarbonate first then wait for a couple of weeks before adding anything else.

By and large I feel that my leaves look healthy, but there is a little bit of browning off around the edges on some older leaves.

Thanks for the tips. I will try them and hope for the best.

I was looking for this information for such a long time as I am also facing same problem with my plants as they are not getting flowers so eblock if you have gone through one of the user tips above and if there is some plant growth improvement then do reply as I will also follow out then.Please give your review as I was also searching for this information from long time

Like others have said, Maxicrop plus Iron will cover most of your trace nutrients. In addition: bury some banana peels every now and then for potassium. Bone meal or even bones from the dinner table adds calcium and phosphorus. FInally, make sure you are feeding your fish good organic fish food and keep pH a bit higher -- like 6.8 is ideal. Here's a post I wrote about getting all the nutes you need here: http://www.farmxchange.org/fish-friendly-fertilizers/
Good luck!

Have you considered the photoperiod? That is the length of time your plants are in light?
I suspect your lights might be on too long or other light may be hitting them.
In reality it is the length of night/unbroken dark that matters, not the length of the day/illumination.

If your plants flower or fruit in summer you need a short night length (long day).
If they fruit/flower in winter you need to keep the night to 14/16 hours (short day).

A single flash of light in the night period will reset the plant's timer so to speak and turn a long night into two short nights, if that makes sense?

That makes sense, i have seen it said in other grow forums based on other plants.
however, how does that work when outdoors in a city, for eg. ive been going out at night when i get home in winter with a torch. There are also streetlights that shine into my backyard, what effect do these things have on plants? much?

I've wondered the same thing. And pondered planting coconut palms beside the fence near the streetlight... They almost never fruit in SEQ.
The biology textbook that I remember the photoperiod info from also mentioned that experiments have shown that only one leaf needs the uninterrupted darkness to induce flowering in long night plants.
So maybe a proportion of leaves are in permanent shadow from the fixed light sources?
While I'm on about it they also mentioned an experiment where two plants were grafted together and gave one a long night and one a short night.
Both (of the long night plants grafted together) bloomed even though one was out of season so to speak.
I was a huge biology geek as a kid.

I don't see that you gave any specifics on your lighting but another issue may be the color spectrum and intensity of your lighting. I had to switch from metal halide and T5 to Hortilux high pressure sodium lamps to get fruiting on my indoor system. On/off time also has a role to play in it.