Backyard Aquaponics
A place to discuss aquaponics

I am thinking about using a free hottub for my system, but I don't want to buy 500+ gallons of growbeds and a pump that will circulate 400 gallons of water. I was thinking about a raft system. How many plants do I need for a 300 -400 gallon tank stocked with trout? (Maybe 50-100 trout) What plants can be planted this way? What is the floaty stuff made out of? Would Styrofoam work? How do you start seeds? Do you still need growing medium?

i think you will need a biofilter and clarifier....

Styrofoam is used, but some kinds will asorb water.

That's a HUGE density, I would say you will definitely need a bio filter and clarifier or at the least some sort of solids removal. You would still need a pump to move the water through the fliter system. You may consider going with a set of vertical or horizontal grow pipes. That would work for both a filter and solids removal. You could also float rafts with lettuce on top of the fish tank to further help remove nutes.

Froggi,
Your need for a growing media, and the type you use, will depend upon whether you are just using the foam as a flotation device and the kind of plants you are wanting to raise. Some folks are raising aquatic plants free floated in the water, so it all depends on what you want to do.

If you are wanting to raise lettuce/herbs you could use mesh pots or auto pots set into the foam blocks, and will need some growing media for you plants to start and stabilize themselves in.
Kevin

By all means you can grow plants in a raft system in little or no growing medium.

HOWEVER, you have the ratios thing a bit out of perspective. It is not the number of plants that will sustain your fish but rather the volume of growing medium or biological filtration. You could run a huge biofilter and no plants and the system will be happy, but definitely not the other way round. In 400 Gallons (~1500L) 100 fish is pushing it without at least 1:1 bio filtration. Ie you need the equivalent to 400 Gallon of gravel.

I think people forget here that the key to aquaponics is NOT just the growing of plants in fish water. The key is the conversion of lethal fish waste to a usable form... nitrate. A byproduct of the nitrifying process which plants can use. Aquaponics is not the magic solution which some people believe. It won't allow you to keep high densities of fish without the correct and essential filtration.

Floating raft UVI style works on the theory of requiring 1sqm of raft growing area per 45g of daily feed (if my memory serves me correctly). Now that is assuming a 2% of fish mass feeding rate, and removal of all solids, with biofilter in the system.

So assuming you had 100 trout at 500g, thats 50kg at maturity. Feeding 2% of mass per day is 1kg of feed, so thats 22.2sqm of floating raft.. With biofilter and solids removal...
Assuming I got my maths and figures correct..

Thats a lot of Polystyrene....

Tim, thats a big call, what happens when the nitrates go through the roof? then it turns back into aquaculture with the water thru put

Hey LF.



I always get seedlings (from bunnings) for my DWC. Or i grow the seeds in gravel and then transfer them across. Seedlings defiantly works best!


For the Polystyrene.... i get mine from the local Chinese shop, they always have some out the back of their shops! Or,the supermarkets are always dieing to give them away!

VB, stock up for any possible floods or typhons? (I know, surf board supplies. )Kevin

I should have written that Steve. Basically I was just tring to get the point across that you cannot have aquaponics with just plants and fish alone.

Without plants the nitrates will go through the roof, but not as fast as the ammonia in the plant only setup.

I believe it is possible to have aquaponics with just plants and fish alone -- with water, of course. In a sense, the UVI system is that. Aparently with NFT and the raft system, the roots provide the substrate for the bacteria

Yep ... it's called DWC.... needs high flow rates to provide oxygenation...