Backyard Aquaponics
A place to discuss aquaponics

Hi I can only find pump size recommendations relative to the volume of water you need pumped per hour. Does this mean that if you are only pumping for 15 min per hour on an ebb and flow you need to quadruple the pump size to ensure that the you pump the whole volume of your tank per one hour cycle i.e. in 15 min?

Also I have 2 x 4500 tanks but my grow bed volume is only 4500. Will the nutrient level be too dilute for my veg if I only 1/2 stock the fish tanks?

This is my first post but my new obsession so hi everyone can't wait to post more. Have a borrowed excavator so I need to get back to it but will update soon.

Yep!...
You should stock fish in ratio to your GB volume, not FT volume.

Even if stocked with fish to your maximum safe stocking density IMO the nutrient level will be on the low side, but not dramatically so. I would consider reducing the amount of water in the FT's.

St Vinnies has a 3000L tank... 6 x 500L grow beds (3000L).... and only 100 fish.... and the plants are growing just fine....

I have a 6000L tank... 4 x 500L grow beds (2000L)... and only 20 fish... and the plants are growing just fine...

Thanks for the advice! I was planning to have one tank for mature fish and one for fingerlings Or maybe ond tank for different species. I might give it a bit of trial n error as to the stocking rates.

Any ideas about the pump?

You're such a w-nker Rupe!...

Last week a 2:1 gravel:water ratio was the go, but this week 0.5:1 is perfect???

If he can reduce the water level in each FT to say 3000L, so a total of 6000L of water to 4500L of GB... what would the problem be in that?

As you said yourself Yabbies.... stock to grow bed filtration capacity.... the fish tank volume has nothing to do with it....


So the above is immaterial.... and totally unrelated...

(And my reference to the "ratios" was in a "historical" context... and related to specific "historically" suggested stocking levels.... and more particularly... to distribution of wastes vs grow bed maintenance... nothing to do with this what so ever...)

The ammonia wastes being produced by the fish... are constantly being produced.... and constantly recirculated....

Directly related to amount of feed... (number of fish to an extent).. which produces an amount of ammonia (and some other wastes)... which (assuming total conversion) produces an amount of nitrates.... that is capable of supporting an amount of vegetables...

The equation is that simple.. and concise... no mention of water volume what so ever...

If the fish are stocked to the filtration capacity... the "nutrients" wont be measurably "diluted".... nor will they be "measurably" increased... by lowering the tank level....

I laughed because I've seen a couple of examples where this has been done/recommended... including one where the level in a 1000L tank was reduced to about 300L... because the fish were "small"... They died....

Soo... I will need a 36000 l/h pump? Surely this can't be right? Or is it?

Also if I only have half the volume of growbed to water, that means that I should only stock fish to 1/2 the recommended stocking density. That would mean that the nitrogenous waste would be half as concentrated presumably. So will the plants simply take up what they need or will they be lacking in nutrients and not grow as optimally as in a system with equal volume tank to grow bed? I.e. will I be at a disadvantage by having the extra water for the fish (I really can't have more grow beds at this stage).

Hi Colours, I wouldn't worry too much about the semantics. I successfully (along with many others) run a system on F&D without pumping all the water in the tank each hour.

I run F&D on a 15 mins on and 15 off up until recently with an 8000/l pump that was probably only moving about 6000l/hr when you took into account friction etc. My system is 5000l of water made up of a 4000l main tank and a 1000l sump with nearly 3000l of beds). At best I would be putting only 3000-3500l through the system per hour. I have successfully grown fish. I test pH every 3rd day and ammonia every second or 3rd day while I have trout (this is when the system is pushed the hardest). It works fine. I'm sure there is a reason for pumping the full tank volume per hour but in the bigger systems pumping less seems to work just as well.

(just for those that follow my system thread I have recently installed a 12000l/hr pump but that was more for the additional head not volume and it still would not be pumping the tank volume through the beds per hour)

I doubt that any of the BYAP installs with the 3000l tanks have 12000+l per hour pumps (they generally run 15 mins on 45 off.)

Lets break this in 2

1/ "Recommendation" is to turn over FT volume once per hr. Some do it less with no issues and believe Aquaculture'ist like to do it at least twice. Your pump - whats the head height you are looking at to pump and yes, its to small for 1 FT let alone 2 if your going timed (with a zero head, you will pump 900 litres per hr - you have 4500 litres to move). If you went Constant Flow, it would be better

2/ Get this sorted before you worry about stocking levels

They don't However, they do better than 1/5 as per the OP

It will work - no doubt however you know where to look when you cant move your solids (if you stock accordingly)

When writing my last post something in the back of my mind was nagging me that I had read something about this some time ago.

A search found one of Dr Wilson Lennard's papers on Aquaponic System Design Parameters - Fish Tank Shape and Design that had the info, some of which is reproduced below http://www.aquaponic.com.au/fact%20sheets.htm

In fact... depending on density... it could be 1.5+ times per hour...

I concur John

So to the OP - no go sunshine