I use a bell siphon on my outdoor aquaponic system and I'm wondering how often I should flood and drain the growbed. Is there a general rule of thumb?
With my pump, the bed fills up in about 12 minutes and then drains in about 3. I initially had the pump going continuously (24/7) but I was concerned that the plants might be getting too much water. Specifically, my peppers started getting some yellow leaves w/ small black spots.
In my indoor aquaponic system, I have the beds flood for 15 minutes every hour during the daylight and my peppers do great. So I decided to do the same for the outside system and I installed a 15 minute timer and now have it flooding just once per hour (about 15 minutes) during the daylight. Plants seem to be doing well, but there's a little yellowing still on some leaves that I'm concerned could spread if I don't get the flooding right.
So is this enough flooding? Too little? Should continous flooding and draining 24/7 work?
Some notes about my outdoor system, for what it's worth:
I don't think the frequency of flood and drain is what is causing yellowing leaves. There are systems I know of that run continuous flood and as long as the water flow is enough and there is enough aeration most plants do fine with it.
More likely you are seeing some sign of deficiency. Can you tell us more about the yellowing leaves? Is it the older leaves or new growth showing the yellowing? Is it the whole leave yellowing or are the veins staying green longer?
Have you dosed with any seaweed extract or chelated iron? What kind of fish/how many and what kind of fish food? How big is the system?
My first guess is Iron deficiency with the pH up between 7.5-8. A dose of chelated iron can help and as the system matures you should see the pH come down. Iron Def usually looks like new leaves yellowing but the veins stay green.
I worry with systems that don't pump overnight since the fish still need filtration and aeration so if you system has very many fish you may run into problems having the pump off overnight as summer goes on (warmer water, bigger fish can use up aeration and build up more ammonia going overnight without filtration.)
Thanks for the fast responses. The yellowing is happening on the older leaves. In the case of the peppers, it's worked its way from the bottom of the plant upwards. The leaves start at a deep green and turn a yellowy brown with a few blackish spots. The yellowing seems to happen evenly, so the vein didn't stay greener longer. The cucumbers look good, but compared to the squash all their leaves are a lot lighter green.
I have a 160 gallon tank with about 80 comet goldfish, about 1-3 inches.Attached are about 85 gallons of growbed (12" deep).
From your information and a little Googling, my guess is that the peppers got hit with some type of disease (we did have a very wet start to season here while system was on the continuous flood and drain too) but that I do have iron deficiency in general too. I think that iron deficiency makes sense because I didn't have the fish in the system until the plants went in. So while there is plenty of nitrate, there's not many trace nutrients like iron built up, plus pH is a little high making it difficult to absorb what is there. I will probably grab some chelated iron today and I might just replace the pepper plants because it sounds like they might have an infection.
And good idea on running the pump during the night for aeration/filtration. I'll probably put it on at least for a few cycles at night. Thanks!
The first season in an aquaponics system can be a bit hit and miss as to what will thrive and what might be better off just pulling out.
I will caution about using hydroponic nutrients in with fish since the salt levels can build up if you do that and there are things in hydroponic nutrients that would be detrimental to fish if used too much (zinc, copper etc.)
not sure if this will be helpful, but if it is only the lower leaves, it may be a deficiency of nutrients? i only say this because my plats are doing the same thing...i had a 32 year college horticulture professor take a look and he explained how the plants will use all the energy and nutrients it has to grow its new upper leaves, while neglecting the lower older ones, therefore they begin to turn yellowish or even like mine, get crisp edges....this is a question im trying to solve right now...so good luck!
Just be careful about over doing the nutrients, though...even worm tea. Since this is a closed loop system what the plants don't take up will remain in the system and not wash away like it would in soil.
Hey Richard, are you settled in your new home now? Setting up AP systems there?