Backyard Aquaponics
A place to discuss aquaponics

I have read Joel's book so feel I am pretty well versed on the concept of flood and drain, however I am a bit unclear on 1 thing and it is particularly relevant when operating a small tank system flood and drain, such as my test setup (350-400 litres):

- To flood the grow beds, a certain amount of water is needed. After flooding the beds, this water returns to the tank to make it full again. At the point when the beds are full, the tank will obviously be down by the amount of water that is in the beds. My test bed will have a capacity of just under 600 litres. Obviously the majority of this will be taken up by gravel, but there would still be a substantial amount of water in the bed when full. My question is, approx how much water would be in the bed when full? I am concerned about what the level of my tank will be when the grow bed is full. May be quite shallow for the poor fish

How long and how often do the beds have to be flooded?

I guess flood several times a day .. and dump asap would be good .. won't casue the fish too many probs being in shallow water for a short time maybe?

Probably depends on the water retention character of your growing meduim .. but I am totally new at this .. so I am learning ..

Maybe make sure that you have a bubbler and air stone working well, if not consider a larger holding tank ... or connect another to it .. just to give ya some extra "water mass", chemical or thermal . .

Maybe at low water level keep the air pump going a a low flow rate .. but efficiently airating the water ..and make sure the fish don't have a quick temp change ... ensusre that the fish can swim arond and that they don't don't get stressed for too long, changes of temperature, oxygen depeletion etc. etc can kill real quick .. etc. etc .

I am a newbie .. just guessing ...

Ahhh, something that used to worry me a fair bit too VB... My gravel has about 20% air space, or water space between the particles. This is easy to measure by pouring a known volume of medium into a container, say filling a 9 litre bucket. Then measuring the amount of water it takes to fill up the bucket to that same level.

If yours is similar to mine then a 600L growbed will take about 120L of water to fill, lets round it off to 100 as you won't want it to be to the very surface of the gravel, in fact it may even be a little less, perhaps more like 80-90L.

If your tank is 400L and it needs to pump about 1/4 of the water into the bed to fill it....

But you will need to check your medium to see what water space you have between your medium particles.. Keep us informed as to what your medium air space is....

Joel