Backyard Aquaponics
A place to discuss aquaponics

Greetings All

I may have oversized my pump

However I question even this, because my pump is currently able to just pump enough to the top of my NFTs and all my dutch buckets. So I think my size is okay

My Pump connects to 2" PVC

But the problem I have is the 2" valve leading from Sump (single Pump) to the fish tank is about
3/4 closed
the 2" line decreases to 1" just before entering the fish tank (water coming in)
and the 1" leading into the actual tank also has a valve that is 3/4 closed.

Reason:: anything more and the fish tank overflows.
Basically I can put more water into the tank than I can take out of the tank use a 1-1/2" SLO


How Can I increase the amount/volume of water exiting the SLO (basically vacuum out the water, in increase the suction or vacuum effect of the SLO ? ? ? ?

Currently SLO and Drain (from bottom of fish tank to RFF is all 1-1/2" PVC

I have thought of connecting the 1-1/2" SLO into a 3" drain line and have 3" PVC into the RFF and Bio Filters
But Keep the SLO (inside the tank) as 1-1/2" because that's the bulkhead I have.


Fish Tank is an IBC Tote and I can not safely increase the Bulkhead size and ensure a good seal
Thus I don't think I can change the Up pipe size. of the SLO
However I can Connect the SLO bulkhead into 3" PVC and have 3" PVC into the RFF and between the RFF and Bio Filter.

I need more suction in the SLO, but don't know how

Thanks in advance

Hi Bear,

You say the 2" valve leading from Sump (single Pump) to the fish tank is about
3/4 closed, you could put a "T" after the pump running water back into the sump and control the volume to the fish tank, that would stop your overflow.

How Can I increase the amount/volume of water exiting the SLO (basically vacuum out the water, in increase the suction or vacuum effect of the SLO ? ? ? ?

I have thought of connecting the 1-1/2" SLO into a 3" drain line and have 3" PVC into the RFF and Bio Filters
But Keep the SLO (inside the tank) as 1-1/2" because that's the bulkhead I have.

Your 1-1/2" - 38.10mm SLO is way, way TOO SMALL, you need to be able to increase the size of the SLO, either by replacing it or adding a second larger SLO and then just run the excisting 1-1/2" SLO to your NFTs and dutch buckets.

I need more suction in the SLO, but don't know how

Your SLO is just an overflow, nothing more, it's overflowing from the bottom of your fish tank instead of overflowing from the top. There is no magical suction, it a plain and simple overflow, for example 100 gallons per minute is pumped into the fish tank, 100 gallons per minute needs to leave the fish tank from the SLO, any more volume and it will overflow from the top of the tank.

The best way to control the volume into the fish tank is by using a "T" rather than throttling the pump back.

I run 2 x SLO's side by side, they are both 90mm - 3-1/2" stepping down to 50mm - 2" PVP Pipe, it wasn't setup originally as a dual SLO, I added extra grow beds to the system and needed to divert water across to them and because my plumbing was already small at 50mm - 2" PVC, so I just added the second SLO and a manfold.

I found that stepping down from 90mm - 3-1/2" to 50mm - 2" and the second SLO made sure that the smaller 50mm plumbing runs at a 100% capacity and has plenty of volume through the filters and grow beds.

The Slo's are screwed and not glued so they can be removed for havesting the fish.

joblow Thanks

DSCN1545 4th Image Appear you have large SLO pipes that are reduced as they go through the IBC wall
Is this correct ?

Also Can you say what is the dimension of the piping in the 4th and 5th image ?
4th appears to be the SLO ready to exit the IBC tank
5th appears to be the SLO on the outside of the IBC tank
Also what are the dimensions of the bulkheads in 4th and 5th images

Thanks again

Yep, similar to above, why not just add another SLO..

Ive found a 50mm SLO plenty big enough on IBC fish tanks

I have measured 1200 Lph going through a 50mm DWV SLO

Mine have stayed clean one corner gets a bit of waste settling this can be fixed by a short horizontal leg on the bottom set in the right position

Having said that I only use them as temporary tanks and sumps after using a round slope bottom aquaculture tank I think they have their limitations but of course $$$ are the first consideration.

Flow through the SLO can be restricted by not enough holes / slots in the pipe at the bottom (Water cant get in)

Flow can back up because the water cant get away (too many bends and or taps that restrict flow)

Or I found out the hard way when a tank sunk a bit not enough drop away to the grow beds (Water backs up)

Yes a second SLO will do the job but of course if your gushing water through the tank a lot of feed will end up going out as well

So again it depends if you want to run high fish numbers in the IBC you will certainly need lots of flow through the tank

First thing measure your flow into tank

joblow thanks again

Terra I don't think I have a flow rate problem last time I measured the flow out of the IBC fish tanks was around 860 gpm.

It's just having a 2" (50mm) line from the pump and 2" teed to the grow beds valve fully open, and the 2" line to the fish tanks with the valve that is 3/4 closed.

I can get more water into the fish tank, and thus have a higher flow rate, which by my readings and understanding would promote healthy fish and allow for higher densities.

I had never heard of or even considered multiple SLOs That seems like a wonderful idea.

As I stated at the beginning. My water flow through my fish tanks are restricted by the water flow OUT of the tank via the SLO. I can't safely increase the bulkhead size. But had thought of dumping the 1-1/2" SLO into a 3" line between tank and filters.

I have also "lost" small fish through the SLO and found them in the filters, which I have netted and put back into the tank. But as soon as they are big enough that problem goes away.

Thanks Guys I will certainly look at replumbing the line out of the fish tanks and adding a second SLO

Thanks