For the aquarium and hydroponics idea, the plan is to pump water through a gravel filter at the bottom of the aquarium, where beneficial bacteria will apparently colonise, sort of rudimentary biofilter. Once the water has passed through the gravel filter it will be pumped at a low flow rate onto a piece of glass on a slight incline, so that there is a film of water falling down from the top of the slope to the bottom (the film of water will be 1-3mm deep).
When the water falls off the bottom of the pane of glasss it will fall, in a sort of waterfall, back into the aquarium which will oxygenate the water as it falls through the air and hits the water. The plants (tomatoes I have selected, along with one or two cannabis plants like an autoflowering strain) will grow on the plate of glass with the roots taking up the organic nutrients from the fish faeces supplying nitrogen and other nutrients.
Because it will be done in the greenhouse, the plants will grow from natural light, but I'm thinking of supplementing it with a T5 shop light or a small 250W HPS lamp. The roots will clean the water of nitrogen compounds, making the environment better for the fish to survive.
I need to know two things. What should I feed the fish? Bearing in mind, what goes in must come out, so I want to give them a really nutritious food rich in trace minerals etc. What would you recommend? Is there some type of fish food based on seaweed? It must be relatively cheap, as I don't want to waste any money, and if it's possible, I'd love to be able grow the food that they eat. Is this possible?
Secondly, how do I know what rate of plants to talapika fish to use to the number of plants that I've got growing? And because the plants will be removing the nitrogen from the water, do I need to regulate the pH of the tank water? And as for the talapika fish themselves, are they actually need to get a hold of? Can I buy them easily from pet shops? Or do I need to order them in from some specialist store? Can I buy them online and have them posted (forgive me if that's a stupid question)? Or if a normal pet shop didn't have them, would they normally be able to order them in if I were to request it?