Backyard Aquaponics
A place to discuss aquaponics

Great thread Lettuce,

I'm planning on doing a headless SLO, RFF, bio-filter combo and use air to drive it. I want all my pump flow going to my grow beds.

I'm planning on separate filter and grow-bed circuits. The filter circuit exit the tank just above the SLO and then enter the RFF from the RFF to the bio=filoterit will re-enter the tank far enough below the water surface to use an air lift to drive this circuit

Lobster man Charlie,

I have seen figure floating around a lot too. That is the standard for systems with IBC tote fish tanks that are 330 gallons (1250 Liters) or more, right? I'm wondering how to scale that down effectively. I can only assume that the people using 3.5 inch (90mm) pipe have flow rates upwards of 400 GPH (1500LPH) coming from their pump to effectively push solids. Personally, I'm at a bit of a standstill building my system until I can find what pipe diameter will be best.

3 1/2" is used here often because of the cost, at $12.50 for 20 ft.
Even if you use a larger pipe diameter, the draw is governed by the inlet size at the base of the slo.
A larger size allows for upsizing the pump and guarantees no overflowing of the ft.

This cannot be true, once the water hits the main pipe diameter it will slow down. Say you had a 10" pipe with a 1" fitting conversion on the end, once it hits the vertical 10" section, the solids will not be able to travel up the stream because the flow is dispersed across a larger area. I want to make sure this effect does not happen with the pipe that I choose.

Sorry Lettuce, Steggley is right on this one, doesn't matter the size of the pipe as in going large however going small is not as good. So bigger the better, 90mm is the GO.
The flow might be slower but its volume is still the same or slightly better.
See my SLO, this works an absolute treat, i don't get any crap on the bottom at all and i have Yabbies on the bottom that are fed Lupin, my only problem is keeping all the lupin from being sucked up. I am pumping 5000l p/h and this keeps up fine and sucks the crap fine, when i add water to the system i usually put the hose in the FT full blast and the SLO still keeps up fine, the water level increases but so does the flow.

The fact still remains that if the pipe diameter is too large for the given flow, the pressure will not be great enough to push the fish solids up. Doesn't matter what you do with the inlet, if the diameter is too great at any point in the vertical pipe the solids will drop out. I'm only pumping at 225 GPH (850 liters per hour) which is almost 6x less flow than you have. If I used that pipe, I would probably have issues sucking up solids.

Fair point regards going ridiculously LGE on the lifting section of the SLO but in the range up to 90mm then bigger the better. 90mm is perfect and absolutely tried and tested on this forum, especially at and around 5000l p/h.
Bare in mind also that the solids are not like little pebbles or anything the like, they are just below neutrally buoyant (or there a bouts) so doesn't take much to move them at all.

Hmmm, good point about them not being like rocks. Yet I do not think that 90mm would be a prudent choice for me. If 90mm works perfectly for 5000l p/h then something tells me it won't work for my 850l p/h.

Not sure mate but my guess it would still be fine, just need to limit the intake size. 850l per hour in 90mm will still have some reasonable flow. If you top your system up at the FT from time to time this will also assist in flushing the SLO.

I'm leaning towards 50mm (2 inch) right now. This is really holding up my build process to be honest. Installing these pipes involves drilling several bulkheads that are permanent and somewhat expensive so I don't want to get it wrong. (can't go with uniseal because of wall thickness) I think I need an engineer

If thats the case it is easier to reduce from 90mm but you can't increase meaning to could put 90mm through the wall and reduce to what ever on the lifting side?? But i still think you would be best off going 90mm all the way then reduce it off to your GB's.
As for unseals and wall thickness i fitted them very successfully to the IBC's and they don't have much wall thickness at all.

By wall thickness I mean really thick compared to IBC. The wood is 1.5 inch (38mm) thick.

Mmm not sure of your set up but you wouldn't be fitting any fittings to the timber frame?? If you need to cut a hole through the timber at 110mm then a 90mm hole in FT then fit the unbid seal?

That's definitely an option. I wonder if bulkheads would be better in the end though.

Charlie - not for a 1000l/hr pump. people do need different sizes man.

Lettuce - No SLO has the ability to move solids across the tank floor, you must rely on your fish to move the solids around and when they land/move close to the slo inlet, they get sucked up. a lot of people run catfish too to help with this.

You can also balance out a larger flow with a smaller pipe by lowering the outlet height and letting the pump create more head.