Backyard Aquaponics
A place to discuss aquaponics

I'm using a 50mm SLO running diagonally across the bottom of the FT with slots cut every 60mm apart using two 45degree elbows to aid the uplift but I'm not sure how well it's performing. I understand that the FT wont be as clean as it would be with a pump drawing up the solids and I'm not sure if I could be running more efficiently than I what I have in place now.

Would I be better off adding 6mm - 8mm holes between the slots to improve the take up or changing the diagonal pipe to a 90mm with a 50mm vertical pipe? Or even just running with a vertical pipe in either 50mm or 90mm stepping down in size to the current 50mm overflow.

In the coming days I will be adding a 65L/min air pump with one and possibly two 5" diam air stones, will that aid the solids uptake?

The air stones will not be inside or connected to the SLO in any way they will be just sitting on the bottom of the FT.


That photo of the FT was taken while the pump was still in the FT and pumping to the grow beds so the FT is not that clean anymore.

What is your pump (litres per hour at operating head height)? How are you returning the water back to your fish tank?

I ran an SLO with slots like that, it got blocked.
I have now gone to an open ended pipe that sits in the middle of the tank, vertical, 1cm off the bottom.

What is the width of the slots? I used a 5mm thick disk to cut mine - no blockages with over 18 months of use.

Arbe it's a HQB-3503 3000l/h with a maximum lift of 3.5m and it's pumping from the sump to the fish tank through 19mm hose.

It looks OK to me, if it's not performing well you can chop off some of the length. (Less holes = more suction)
The fish will tend to keep things stirred enough to get it to the SLO.

Your pump sounds like the right size for your system - I would guess you have less than a metre of lift/head. The 19mm pipe may be limiting you a bit.

Do you have the water returning to your tank to make the water swirl (as much as you can with a square tank)?

I agree with Arbe, Id up the output pipe size.

Use 50mm pipe, a 45 deg elbow or 2 and an 45 deg angled cut on the end of pipe so it can sit on the bottom in the centre.
Increase flow rate of you want more suction
If you really want spotless tank use a 12W wave maker pump to push water in a circular direction. Rubbish tends to the centre where the suction is
The slotted pipe will DECREASE suction and is possible to block up I think

Thanks Guys, when you say increase the output pipe size, you mean from the pump to the Ft.

Yes. Increase the pipe size from pump to fish tank.

ArBe the lift/head is less than a meter high.

ArBe & Jet there's only a venturi swirling the water at the moment I'll need to add something extra.

I'll need to be careful how I go about it, I had to throttle the water pumping into the fish tank because it was overflowing and pumping the sump dry, so I can't increase any water being pumped into the FT anymore than it is now.

Jet I'll research Wave Maker Pumps or even look at just running a small pump in the FT to circulate the water only.

Mind you it's pretty cold here now and the fish aren't all that active so there's not a lot of action going on to swirl the water.

Thanks ArBe

Was it overflowing the tank because of the SLO being too small though?
When i say too small, i mean you dont have enough slots/not big enough slots with little head above the top of the SLO, meaning that the water is flowing in faster than out....

Or is it simply that you bought a pump twice as big as all of your piping?

What size pump do you have? i have run close to 8000l/hr through 50mm pipe easily.

If your fish tank is overflowing and your sump running 'dry' then install an overflow pipe from your fish tank to your sump which exits your fish tank slightly higher than your SLO.