Backyard Aquaponics
A place to discuss aquaponics

What does "SLO" mean?
Just to make it clear, you are saying that it takes 15 minutes to drain the whole GB, assuming you use FD, right? Would larger pipes accelerate the process? Standpipe being 40mm and then the return 90mm, still have to figure out how to connect this two diameters... More likely will need 3 ou 4 reduction until I reach the right size.

In the meanwhile I came across another problem. I just realized my actual pump won't do it. I need to start shopping for a new one. Let's assume I buy a 2000L/h pump, 38 watts, max height of 2 meters. If the pump is pumping the water from the FT one meter high into the RFF, what should the flow rate be? I'm assuming the 2000L/h is only true when no height is added into the equation.

The "weak"pump seems more of an issue now as you've raised the RFF outlet above the GB inlet.
An Aquagarden Mako 4000 Lt/H pump will pump about 3600 Lt at 1.0 m head but you may have to raise the RFF outlet to be able to avoid water backup as it tries to siphon through the UG pipes.
You should test your pump to see how much water it can pump in how much time at what height.

"SLO" means Solids Lifting Outlet which is a pipe that usually hangs vertically in the middle of the FT and has a fitting on the end that allows muck(solids) and water to enter but not fish. It bends near the water level and exits through the side wall and continues back to the GB or in your case the RFF.
When the pump in the sump comes on the and fills the FT it will raise the water level about an inch while pushing water and muck in the bottom SLO fitting then over flows out to the GB. A T fitting at the top prevents siphoning.

I use a 20 mm poly tube to deliver the water to the FT and a 40 mm return to the GB. These are the minimum sizes I would go as my lines are just a few inches under ground and easy to get to. Other members have got them much deeper and more awkwardly placed and wished they had pits etc to service them.
My F&D systems run the pump 15 min on 60 off which fills the GBs in less than 15 min and gives them an hour to drain.
I like this method because it drains all but 2 inches(reserve nutrient bank) out of the GBs drawing oxygen in behind the dropping water, reduces the possibility of dead zones, saves power and reduces water noise.

SLO = Solids Lifting Overflow

Again, thanks for your invaluable help.



I can see another advantage of having an "oversized" pump like you might have, assuming all water in your system is being cycled in 15 min. Since the flow rate is high the water is travelling at higher speed, thus reducing chances of having muck settling in the pipes and GB medium. I like the idea. In the end the system spend the same power as the tipical 45min-15min cycle but has other advantages. Only downside is the higher upfront cost of the pump.

In my previous system I had a 20 mm poly tube connected to the outlet of the pump as well, it clogged more frequently than desirable. Unfortunately I couldn't upgrade for a larger tube or the flow rate would be reduced since the water weight in the tube was higher.
This time with a larger pump I wish to have at least 25mm. Good thing about poly tube is that it makes life much easier for adjusting and maintaining the system, it must be said though, it's harder to clean vs PVC.

I think in my situation a SLO won't be needed if the pump is placed on the bottom of the FT.

The RFF would be side by side with the FT, the poly tube wouldn't be underground.

Yes I like the poly also because it can have large radius bends and long runs.

I think the idea behind the slo is good as it drags the heavier nutrient rich water from the bottom of the tank while replenishing the upper levels with cleaned water. But unless the bottom of the tank is tapered the slo fitting wont get most of the muck. There are a few designs for those fittings but I haven't seen one completely clean the bottom.
My Sys 3 uses an external pump and pulls the water from the lowest point in a double tapered tank. The fish agitate the muck and it gravitates to the lowest point where there's a woven wire mesh and a one inch outlet and every thing gets sucked out. I'm very happy with it's performance and I'm thinking of building a large FT with similar design.

Having in mind the T shape of my pond, there's a lot of corners where the waste can settle. I'm not expecting to have a clean bottom, instead I will be relying on airstones to help breaking the solids, plus low fish density and low feeding schedule. For me veggies are the goal, the fish has to be KISS. Though I would like to try some aquaponic trout

Hello again,

I just finished some brick work around the pond, it has now 60cm above the soil level which arrises an issue.
Now, in order to have the outlet from the GB higher than the FT I will need to have a very tall GB. 60cm FT level + 20/30cm to unsure good flow rate + 40cm GB depth. 120cm/130cm is maybe too tall for a GB, what do you think about this? Is it practical?

Also, another question. In order to fit the GB nicely in my backyard I would like to keep it long and narrow. So my idea was 3m long x 0.5m wide x 0.35 deep. I wonder if this dimensions could affect in any way the flow rate and/or solid accumulation?


Thanks for your time.

That's too high and would be tough to work with. Sounds like you should add a sump to catch the outfall from the grow beds and then pump from that into the fish tank where the water would flow back out via SLO and gravity to the grow beds.

Use a distribution grid in the grow bed so that the solids and flow go more evenly over the entire bed. Leave any connections unglued so that you can take the grid apart and clean it if needed.

With round fish tanks and water circulation, plus aeration in the middle of the FT, the SLOs in both my systems keep the bottom of the FTs nice and clean. No extra cleaning required. Only with rectangular IBC or other non-round FTs might your SLO not keep the bottom clean.

Indeed, the distribution gird will help.

Concerning the sump tank, that would imply digging very deep since the FT is already below soil level.

What if I had the outlet from the GB going into the bottom of the FT? This way I would get a few centimeters extra by avoiding the pipes above the FT.



I'm not sure if it would work or if the pressure inside the FT would influence the flow rate from the outlet of the GB into the FT.

I'm not certain if what you're suggesting will make any difference. I think it's better to bring the water in high so that you can get more aeration. I think IBCs are around 120cm tall and people do put growbeds on them so even though it's high, doing your bed as originally planned might be the best option.