OK - so speaking of DIY - I've been giving it some thought (which, at this point, is making my brain hurt) and here is my idea. Any feedback is appreciated.
My idea is to build a fluidized sand filter
out of 4” thin-walled PVC pipe, 3' tall. Then use 4” flat PVC caps for top and bottom. I'll use 3/4" bulkhead fittings in the top and bottom. On the bottom end I'm going to plumb in the incoming water (exiting) from the pump (I'm thinking about using a 'Quiet One -Model 1200' pump to circulate the water - need a pump that can be external/dry).
Top of filter:
On the top of the filter I will have a 4” cap with a 3/4" bulkhead fitting in it. I will leave the inside, top; open (no pipe extending from it). On the outside, top, I will have a union and ball valve then a check valve (so there is no chance for siphoning). That will then get plumbed with 3/4" PVC through the wall on the shop side of the basement to the finished side, where the 90 gallon (fresh water) aquarium is located. Then I will have it return into the tank (with possibly a 90 degree elbow).
Bottom of Filter:
Intake Side of pump:
I will run 3/4" PVC pipe with a strainer (protected with a sponge prefilter) from the tank (through the wall) down to the pump. I will add a ball valve (in case I need to disconnect the pump), then I will connect the return line to the pump with a union (for quick access/removal of the pump).
Output side of pump:
I will connect to the output side of the pump with a union connection, then a ball valve (to control flow) then to the bottom of the filter's 3/4" bulkhead. On the inside of the pipe I was thinking about connecting a tee to the bulkhead (maybe an inch above the bottom) and capping the ends. I will have holes drilled in the tee along the bottom and outward edges (but on a downward angle), so the water will be forcing the flow down and pushing the sand up.
I was thinking about using some pea gravel (or possibly a coarser grade?) at the bottom around the Tee, then adding some Ehfi Substrat Pro, followed by 'X' amount of pool sand.
Also, I'm wondering if I need to add airline, say to the middle/top half of the filter or if the flow of water will be enough o2 for the bacteria.
So... let's have it. Feedback/questions/answers? I would like to hear something now, BEFORE I build it, then later when it's too late!
PS - this will be additional to the Eheim 2028 canister that I'm running.