Backyard Aquaponics
A place to discuss aquaponics

I think that this was the major problem with my thinking.



1:2(FT:Media Bed) volume is what you would design for in order to allow for some tolerance in the equilibrium situation you are talking about? For instance, you could achieve equilibrium with 1:1 but it would be cutting it close?

The 2:1 ratio was develop by the late Tom Speraneo. Since it worked EB (Earthbound) copied it and then taught us (The Forum).

Tom was raising Tilapia with densities as high as ~70kg/m3. Tom could do this because 1. he was feeding them a relatively low protein diet and 2. tilapia can handle realy low levels of DO.

In Australia most people feed Barramundi or Trout a high protein diet and generally don't stock above 30kg/m3 although some do go as high as 40kg/m3. Most stay below 30kg/m3 or even below 25kg/m3.

Many people do have ratios of 1:1 but they stock their fish at half the densities given above.

Thank you so much for your help Stuart. I think that I will opt for 1:1 with low stocking density in a cute little system like this then:




Two Questions though:

1)For the Hydroton Growbed (4FTx2FTx1FT) (1.5m x .6m x .305m) being a rectangle, would it be better to divide it into two square sections and have separate bell siphons? Or would it be the same to just drain the entire rectangular bed off of one siphon? The fish waste will be distributed evenly over the area by some sort of grid coming from the SLO.

2) Is it okay to put Kaldness K1 in the sump? I have a whole lot of the stuff...

An easier way to think of it is that you can make your fish tank as big as you want, as long as you stock appropriate to GB (or biofilter) volume.

Kaldness is mainly used as a biofilter media. While gravel does not have a large surface area to volume ratio it does not matter because you need to have so much gravel to provide enough storage area that you vastly exceed the amount you need to work as a biofilter.

You definitely don't need two bell siphons to empty a GB but some people do have multiple inlets to spread wastes around the bed. Personally this has never been much of an issue for me so I have all my water going in one end and coming out the other (GB is .3m deep one end, 1m deep the other 1m wide and 16m long).

Thank you!

I'm only interested in putting Kaldness in the sump because it seems like an awful waste to have a large ~50GAL (190 Liter) sump with only water in it!

Depending on your setup you can make the sump a second GB. If you screen a portion off for you pump it will flood when the 1st GB drains.

Otherwise having the sump just holding water shouldn't be seen as a waste because it makes the system so simple to run and maintain.

+1 for Stuarts commentsLettuce it might be worth a look at Ryan's back porch setup Esp the pre-filtration for his dwc's will try find the link. Ryan of chatterson's farm, this was his first system post ok forums I think, I found he had a well planned system and easy to take a few key ideas and incorporate into your design. Good luck with the system.


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That is why they need to be so big. Remember the GBs primary function is solids storage not solids or biological filter.

Can you expand on this ? I find this concept ,theory very interesting,

GBs can take on four functions:

1. Plant Production
2. Bio Filter
3. Solids Filter
4. Solids Storage

1 is obvious.

2 Gravel beds perform the function of biofilter but if you use various RAS engineering methodologies you quickly find that our GBs are vastly over sized in terms of their bio filtration capacity. One of the reasons that RAS or AP systems where the solids are removed have such small biofilters is because the media they use has double or tripple the surface area of gravel but often their biofilters are a tenth or less (often a lot less) the size of a GB. The main reason for this is that you don't need much surface area to process the TAN produced by the fish.

3. A GB works as a solids filter if it stops solids going in from coming out. It is quite easy to see and demonstrate that GBs can be quite small and perform this function for a while before they become full and then the system crashes which is why...

4. their ability to store solids while they are broken down is essential to their continuous ability to process those solids and release their nutrients into the system water.

If you have the K1 media you might as well use it in your sump if nothing else is going in there. Although containing it somehow might be a good idea since you may want to get it out one day easily.
I have 25L K1 x 2 in two sumps and I contain it within plastic laundry basket which also have aeration to assist the bacteria and to keep the K1 media moving and knocking of old dead bacteria.