Backyard Aquaponics
A place to discuss aquaponics

Hi all,

First post so don't bash me too much if this has all been answered previously please.

I have been playing google and YouTube investigator the last few months and think I'm pretty excited at giving this a good ol crack. With all the info out there this is a list of what I think I need to start up: a water pump that can pump enough to flush the fish tank 1.5-2 times per hour, back up air( my house runs on solar with battery back up so shouldn't be too reliant on the grid) and a radial flow settler.

I can get IBCs fairly easily so was going to base a system around them being the grow beds with flood and drain being the method with bell syphons approx 300mm deep with gravel or blue metal as the media. Couple of IBCs as the sump tanks, pumped up to the fish tank SLO feed into the grow beds .
I have an old fiberglass rainwater tank on the property I bought that I was going to use as the fish tank. I thought it was a great plan until 2 nights ago I measured the tank to add dimensions to my drawing I've made (in Paint so again don't knock it ), and then when working out the volume I went into shock its huge... 4m diameter x 1.8m high... even if I only fill it to 1.2m that's still 15,800 liters ... at 1m deep its 13,200 liters...

I know the usual ratio for media to fish water ratio would be 1:1 or 0.5:1 is there a work around ? for that size fish tank is it worth even using the tank or should I cut it up, remove it , start fresh with a new tank ?
so if moving forward I then modified my drawing and added more grow beds that I could fit in my space. Which then had me worried about the size of the sump tank I would need to be able to fill all the grow beds and not run the ST dry or overflow it.

could I just use a whole ibc full of gravel to add media with no plant in it for extra media?

I'm in Geraldton Western Australia so pretty warm most of the year, fish species I was thinking barramundi or silver perch even modifying one of the sump tanks as a yabbies'/ marron tank.

thanks in advance for any comments / advice

Having a massive tank is a good thing! Its not about the water to media ratio... its about the fish to media ratio. So decide how many growbeds and therefore how much media you wil have, and that will determine how many fish you can have. Search for the ratio of fish to media, it has been discussed extensively on the forum.

Check out PLJ's system, he has a concrete tank of around 50,000 - 70,000 litres! I've put the link below. This should give you some ides of whats possible.

viewtopic.php?f=18&t=12883

yeah like he said, the water volume is not a big deal,
but getting fish out of a 1.8m deep tank could be a challenge!

your design is ok but with smallish and sump and big fish tank
you'll want to be careful you don't run the pump dry or overflow the sump tanks.
you don't have any leeway with the water volume in that system.

If you had the the water tank (or half a the water tank ) as the sump and the IBC's as fish tanks
plus of minus a couple of thousand litres would not be a problem.

Could you cut the fibreglass tank in half? then you got 2 fish tanks...

can you get the elevation of the GB's above the base of the tank?

fish tanks only need to be 600 to 900 deep.

not sure how much area you have to play with but I'd cut the tank in half
so to have 2 x 4m x 900 deep tanks, with 600mm of water that's 7500l each.
ditch the sump, just pump to beds and drain back to tank(s)
even with one tank and all GB's full the fish tank water level will only go down 150 or 200mm

looking forward to the build Mr Turtle,
interestingly I met a Tommy Turtle today, maybe his related?

Thanks mate that will definitely be some reading material. I do get what you we’re saying about the fish to grow bed media ratio rather than litres, I just wasn’t too sure if having that volume of water would act in a negative way by diluting the nutrients in the water too much .

Would the usual ratio be the same for the water turnover in the tank , a lot of what I have read is that the size of the pump should be enough to turnover the full amount of water in the tank 1.5 to 2 times every hour . If I had 15000 litres of water for example then would it mean that I would have to have a water pump size of 22,500- 30,000 litres per hour

The recommended turnover of system volume is relative to the stocking density, as it is the build-up of metabolites (ammonia and CO2) that is regulated by the biofiltration and oxygenation of the water through its circulation. The 1-2 x system volume / hour is based on a high stocking density...

I would suggest that once you have determined how many fish you can have according to how much media you have, you then figure the volume of water that that number of fish would require according to the typical high stocking density recommended... That is the amount of water that you should aim to turn over per hour.

Having additional aeration at times of particularly hot weather would be a good idea, as lack of oxygen is the first cause of disaster if circulation is inadequate, and warm water holds less oxygen while fish and bacteria require more oxygen in warm conditions.

You are right that the nutrients will be more diluted, at least at first, but it seems that this isn’t a problem. There will probably be a long time-lag during which you will be waiting for the nutrient levels of the water to build up. The plant growth might not be great in the first season, especially for fruiting plants. But the positive thing is that after a time the large size of the system will act as a "nutrient bank" which will be much more stable long term... the nutrient levels wont fluctuate as much in response to your feeding, planting and harvesting practices.

great idea slow boat, on chopping the tank into 2, never really thought of it because I thought the fish tank would need to be a bit deeper that round .. but the measured 1.8m of the tank only accounts for the side wall there’s also the cone on the top which is about 1m high. Using the online calculator the tank volume is 22,000L and the cone 5,000L so if I cut the top off fixed up the filler hole in it then both tanks would be filled about 1m deep and could be about 10,000L each.. Awesome idea I’ll go back to the drawing board now.. lol


I can definitely make the grow beds higher than the fish tank, and agree if I had the sump tank suggestion I had it would be insufficient for the growbed sizes

I was thinking would you have one tank slightly higher than the other with a solids filter in between then pump from one fish tank to the grow bed then returned to the first tank , or would you keep the tanks seperate?

Cheers Danny, yeah I’m coming to realise the big volume of water wont be that big a problem and it would probably be better in the long run as i work away on a 8 and 6 roster so I’m only home every second week and the kids and wife will be feeding the fish and keepin an eye on it all in between.

Ive been looking a lot into different species of fish barramundi would be great but not being able to introduce smaller fingerlings i could see being a problem . So was thinking perch as you can add more fish each month as you start to harvest fish out . Or again is there a reason that everyone harvests in one go rather than a few at a time whilst introducing new fingerlings in ?