Backyard Aquaponics
A place to discuss aquaponics

Hello all, thanks for advance.

I am trying to make sure I understand this correctly. Everything I read said for beginners to start with 1:1 ratio of grow bed volume to fish tank volume. I have a 100 gallon rubbermaid fish tank and to get this 1:1 ratio I would need 4 25 gallon grow beds. Now if I do a flood and drain system, I understand as I pump water into the four GB I will get close to emptying my fish tank.

If I used auto siphons I will definately empty my grow beds. Assuming I do not have an indexing valve, how do I make this work with out a sump tank. Do I just go to a .5:1 GB to Tank volume ratio (I am worried I wont filter the water properly).

I hope this makes sense.

1:1 or 1:2 is usually where people start but don't be too concerned about the grow bed to fish tank volume ratio. Your fish will generate X amount of waste, your grow bed must be able to process that amount of waste (and your fish need a certain amount of space as well). There are guidelines that spell out pounds of fish per cubic ft of media in the grow bed - http://www.backyardaquaponics.com/forum/viewtopic.php?f=12&t=6646. To begin you'll probably want to do about half of this number of fish.

Use Constant Flood instead of one of the flood and drain methods. This does away with the fluctuations in the tank and makes it easier to expand the system if you want because you won't need a larger sump or fish tank to do it.

If your GBs are full of media, it takes up anything from 60 to 75% of the volume, leaving the remainder for water. Each 25gal GB will only take about 7 gals, allowing some air space, so you'd pump about 28 of your 100 gals, leaving 72 gals in the FT.

I never even considered the volume displaced by the medium. Thanks.

Also:



Would constant flood be an auto siphon method? Where the pump is always on, and once the siphon triggers it drains? Or would it always be flooding at the same rate it drains?

Constant Flood is always flooding at the same rate it drains and the level in the grow bed and tank stay the same except for evaporation. The pump is on 24/7. Usually the water level is set at the same spot as the maximum flood level you would have if using siphons (there may be a slight difference from this level though). The constantly moving water is oxygenated by movement and splashing as well as just surface exchange. It does not pull oxygen into the bed like siphons or timed flood and drain would but typically this is not a problem. You can add aeration if you feel it's necessary, I never have needed to but there are a lot of drops in my system. Lots of other people here use this system.

Constant flood also gives you more water in the system because you can fill everything up so you get slightly more buffering of temp and pH.

Hope this makes sense.

>> Would constant flood be an auto siphon method? Where the pump is always on, and once the siphon triggers it drains? Or would it always be flooding at the same rate it drains?


'a constant flow system' can be either. If you want your fish tank to stay full without fluctuation then the constant flood simply has water going back to fish tank at the rate it leaves. 24/7.

If you go to siphon then you have to have capacity for the volume of water being discharged each time by the siphon. If you have multiple grow beds and you can get the siphon to fire at differnt times then the water exchange volume will be smaller than a simultaneous flood and drain *BUT that is not so easy to guarantee*.
[hence one reason why people use sumps]


The issue of build up etc in a constant flood can be addressed by making sure your stand pipe is removable and then just removing/loosening it manually every couple of days.

The other option is to use timer flood and drain but not take out the whole volume.
Put the small drain hole a bit higher up on the standpipe so most of the time it dumps about half the grow bed volume and then just remove the standpipe once every couple days (each bed at different times).

** sometimes you want to flush the bottom water out and not back to fish tank as it can be 'dirty'

>> Gungalla answered the volume bit - so as he says your actual exchange volumes are only percentage of the actual GB volume.


>> the filtering requirement will depend on the number and type of fish you have. Food fish typically need more filtration than say goldfish etc.

This is a valid point but I wouldn't bother with lifting the stand pipe every couple of days for three reasons =

1. At low stocking densities your grow beds can handle the solids so it's usually years before cleaning is needed.
2. Fish aren't too keen on suspended solids coming out of the grow beds either.
3. At higher stocking densities you'll probably want to put a solids filter before the grow bed to prevent problems with bio-filtration in the grow bed caused by solids accumulation OR add more grow beds to spread the solids load over more area.

Grow beds are both solids and bio-filters. To preserve a grow beds capacity to do both you need to have the appropriate filtration for the number of fish in the system.

This is why we dont use words like "constant flow" in australia, damn it just confuses people the way people in other countries use different terms dependant on the state, then the city, then the street they live on....

just stick to flood & drain and constant flood, how much simpler language is when people use recognised terms instead of inventing their own.... :rolleyes:

Thank you all for your responses. I hope to get my system build shortly and hopefully have fish in a few months!