Backyard Aquaponics
A place to discuss aquaponics

I think cutting back on the fish food, eating some fish and water changes are the way to go.

It is not going to be a quick fix though because I do keep all the solids which means that there will be quite a lag effect. Many nutrients will continue to be released over time.

The good news is that I've proved something to myself.

What's that?

I too wana know whats that as well.

Stuart, what are your stocking densities/feed rates? I'm feeding ny appx 40 tilapia about 2-3 cups per day, and still can't get my Nitrates over 5-10 Plants are growing great. I have a lot of fruiting plants. Eggplants, peppers, toms. I'm adding high Nitrate(20plus) from a mineralization bucket, but still can't get any higher. I'm nervous to harvest any fish, that will bring my N down even lower.

Where as I'm nervous to harvest plants.

The fish tank has ~8000L of water in it. Its a 10kL tank which I don't run full and the water level varies a little depending on the cycle of the system.

In it there are about ~350 trout varying in weight from 300g to ~700g. The average is around 450 to 500g I THINK. Which would be about 175kg of fish which would give a fish tank stocking density of ~21-22kg/m3.

I was feeding them about 1.5-2kg of feed per day but I ran out a little while ago and I've had a few hickups so they have been on about 1kg per day for the last three weeks on average.

The most number of trout that I've ever run in the system previously has been 200 and apart from my stuff ups it has handled the load this season relatively well. Around GB inlets there has been a bit of a build up of solids but not much. The build up that is there seems to be building up because of the large size of the fish poo. In one bed I've excavated a hole and added an air stone (the constant flood bed) which has done a good job of breaking up the solids so they pass into the gravel of the bed better. This is rather ironic considering my numerous posts about the AQ mantra of keeping the solids intact so they could be more easily filtered. Just shows it pays to not be too wedded to theory.

Basically the beds appear to be able to handle the load but I don't have enough m2 of growing area to handle the nutrients they produce. Once the DWC tank comes on line I should be able to fix this or at least get it to help a bit.

Why so many trout? Just to see what the gravel can handle?

I'd get sick of eating trout every night of the year

I have three people in my family that will eat a fish each.

With 400 fish per year that is only 2.5 meals per week for the year. Add a few deaths and some fish given away plus visitors 400 is just about right. Which is the starting point I designed the system around. It would seem though that I really need to expand my plant growing area or add a RFF

Stuart what is your base conductivity of your water..? as well as pH

Put in a paint filter.

pH was 7 I'll check again tonight.

Conductivity I don't know

Oh you are so nuaghty

Funny you should mention that though. In the Pentair catalogue they have paint filter bags. I was thinking of getting one to help clarify the water in the DWC tank. Its a bit mucky because of all the mucking about I've been doing which has disturbed some solids and all the algae in there. A filter bag would help mean clean it up and get it back up to scratch before I plant it out.

why I ask is if your nitrates is so high it may help if u simply increase the base amount of potassium calcium and magnesium in your system to a higher level.. this I believe should help alot with your problem since the concentration is increased. it should start to compete with the nitrates in system.. and should help growth alot

Have you thought about putting in an anerobic section of the beds? That should lower the nitrates to a better level?

I thought the anaerobic sections happened all by themselves in unfiltered GB systems

+1 Cookie - I reckon alot of my problem with high nitrates is due to not enough other elements (K in particular) which then restrict growth, which then means the plants can't use the nitrates up.

I've observed massive growth spurts after supplementing with potassium before.

I wouldnt do that if I were you and trust me... I experimented alot with anaerobic section.. at such high nitrates the initial amounts of nitrite formation, because nitrates combines with nitrite to form nitrogen dioxide then nitrogen gas, becomes EXTREMELY HIGH because denitrification does need cycling similar to nitrification where nitrates acts as ammonia on this case.. an we all know what happens in cycling when ammonia ppm is high..