Aquaponics - Restricting the feed intake to a system

This post relates to my ongoing electronics project Electronics - PICAXE fish feeder

The feed able to be dropped into the system is limited by the population of bacteria. They are in turn limited in population size by the amount of available real estate on the grow media, and to some extent other surfaces and even free floating within the water.

It's the bacteria that process the fish exhalations and excretions. As fish poop and breath, they add to the ammonia load within the system. The bacteria convert the ammonia to first nitrites, then nitrates. It's the nitrates that most plants enjoy, and the nitrates are not toxic to fish until they are very high.

Ammonia and nitrites one the other hand are very toxic to fish.

So we need to be careful not to overstock our systems with fish, but more importantly, we need to not over feed our systems.

And it really is the system we are feeding, not just the fish.

Generally in aquaponics, we talk about maximum fish stocking levels within a system, but it might be just as useful to talk about maximum feeding levels for a given amount of grow media.

In a small system like mine, I long ago gave up on the idea of eating fish every week. My feeding regimen isn't really about maximising fish growth. I have a set maximum amount of feed that I can add to the system without seeing ammonia and nitrites. When I feed my fish I have a little jar with a level marked on it. I fill the jar to that level each day, and don't ever feed them more than that. I feed them less that that, if the don't want to eat it due to temperature, or whatever fishy reasons fish have for not eating, but they cant ever have more because because the system cant ever have more.

Actually the system can have a bit more, but this way when I find caterpillars and worms and things I can add them at will.

Generally speaking it's also a good idea to run your system below it's maximum feed capacity, so that if something goes wrong, you have some margin for error.

If, for instance, a fish were to die and I didn't notice it for a few days, it would create a huge ammonia spike. That ammonia might take a few days for the system to process, and in my system, I'd get away with it, but if I ran my system closer to it's maximum feed input, an event like a fish death could be catastrophic.

It's ok to run your system close to the edge, but you have to be there all the time, and check it all the time.

I prefer being relaxed.



Not just Aquaponics - Restricting the feed intake to a system - 120 things in 20 years