Backyard Aquaponics
A place to discuss aquaponics

i am helping to set up an aquaponics system out our local high school. We have been given 6 ibcs. we have a seperate 5000 litre fish tank . i want to cut the ibc's to make two growbeds from each ibc. What is the best way to cut each one. i was thinking of cutting them vertically so as to get rid of the lid and the valve as i dont need them. any thoughts or links would be great.

With 5000 litre of FT you would also want a minimum of 5000 litre of media for proper filtration. Cut horizontally and seal the cap with plenty of sicaflex and screw on tight. That way you will get the maximum grow media in each bed.

I have had no problems except not sealing one cap properly which I had to redo. All working well now.

if i cut vertically i concluded i would have more surface area. i dont really need the bulky pallet type base so i was thinking of removing it and putting a peice of steel roof batten down each side.

cc interesting quote about the media. i have a 10000 ltr fish tank and approx 4.5 metres cubed of media and i have had no problems over 6 years. my water parameters are ideal. you have me worried now

Our IBC's are cut the same for the same reason,
But we are opposite with GB to FT ratio.
I run 5k ltr fish tank and have 7 metres of GB and can still get high readings.
It depends on fish stocking along with how much you want to optimise the system

Consider how much water each GB is going to "use" out of the FT, and how much water you require to remain in the FT for the fish and pump(s). You might find you're going to need to use one or more of the IBCs as a sump, or that you're not going to benefit by simply cutting each IBC in two to make GBs. Your water volume is the limiting factor.

GB:FT ratios are bumph; stock density to filtration is vital.

oh i cut them horizontally today so each growbed has a valve or a lid. i was wondering about media. hydrotron is really expensive and the school has a huge supply of 20 mm aggregate. will ibc's hold up to agg.

i am going to have a pump in the ft running to the 12 growbeds. The growbeds will run to a ibc burried in the ground. the sump will contain a pump with a float switch. the incomming water from the gb's will start the sump pump pretty quickly. i dont anticipate that the water level in the fishtank will drop anymore than about 100mm. My home system is set up the same and i have no probs with it. I have friends who raise fish in ibc's and they often have probs with water temp fluctuation and sudden perameter changes. being a school system i want to make it fairly reliable and indestructable. no one will be around on the weekends to monitor it. We were thinking of running maybee 200 silver perch in 5000 litres. In my 10000 ltr home system i have about 35 very large adults.

It looks like you've done your sums, but just to check:
5000L in FT
1000L in ST
12 GBs
2 pumps

Let's assume media takes up 60% of the GB volume, with the water filling the remaining 40%, ignoring a dry layer on top of the GB.

Most submersible pumps will not be able to pump a tank dry, so when the ST is "dry" there will still be about 100L remaining in the bottom when the pump loses suction, so even if your ST is completely full at the start, you'll only have about 900L "usable" from the ST. If you're happy to use 1000L (20%) from the FT, then you've got a total of about 1900L with which to flood the GBs. You haven't mentioned the use of an indexing valve, so if we assume the worst case and that all your GBs flood at the same time with the 1900L (40% of total volume) means you can have 1900/0.4=4750L of GBs; 4750/12~400L each GB. Allowing some freeboard at the top of each GB to prevent the media spilling out, means each IBC must be cut in half, ie 500L each.

If you're looking for a more bullet-proof solution, consider using 2IBCs for the sump and designing on the CHIFT PIST principle, with 2000L in the ST, 5000L FT CHIFT PIST, 1800L from the ST will easily flood the (now) 10 x 500L GBs without changing the water level in the FT and only require one pump either running on a timer or continuously, no float switches.

You can use pea gravel or blue metal (or similar gravels) as media, although they're harder on the hands than the lighter and more expensive hydroton, but makes very little difference to the plants or beneficial bacteria. being heavier requires more bracing though! Do not underestimate the forces and weights involved here.

If you've got 12 x 400L = 4800L of media (filtration) and you abide by the 20 fish per 500L of filtration then your limit is about 192 fish. (If you're going to use smaller/fewer GBs then adjust accordingly).

As you're going install an unsupervised school system, consider security of the power supplies and of course barriers to prevent water entry, backup systems and a remote monitoring system; you mention weekends but what about school holidays and the long Christmas break?