DIY fluidezed bed filter - Mk 1.2 Now Working

[Escher]

Like others around here I considered the fbf long enough to actually have a go. As I have said in the title I think this project needs to be revised.
In any case here is my experience so far.
After researching the web and my garage, the plan looked simple enough and I decided to go for the pipe construction. I had a 100mm pipe long enough to fit under my stand from the floor. I bought two end caps and screwed in the inlet in the middle and the outlet on the side. Then cemented the lot.

[Escher]

I wanted to see what would happen in the pipe during operation so I decided to make some small windows. I cut 3 strips of perspex about 4mm thick. Then I angled the long edges with an angle grinder so that they would fit snugly inside the pvc pipe. Before you do ANY work on the perspex, make sure you cover with masking tape any area you don't want scratched.

[Escher]

Cutting the long holes for the windows was quite easy with a jigsaw. Just smoother the edges and leave at least 20mm of perspex either side to be glued later.

[Escher]

The inlet should have a pipe from the centre going up to 5 mm from the bottom end cap. I thought I would ease the water flow and reduce the sand inside the inled pipe by placing a small cone on the bottom end cap. (I just went through my son old toys and found a small spinning top!)

[Escher]

Time to cement the pices together. Start with the windows by applying cement to the inside of the pipe and the angled edges of the strips. This is messy so wear disposable gloves, turn the pipe with holes toward the ceiling then apply the strips to the pipe by holding them up from underneath . Keep pressure for a few seconds, then it will stay.
Wait for 24 hours then apply silicone over all the internal edges. Don't leave any gap. No gaps = no leak & better flow.
Next cement the top end cap (the one with the inlet/outlet) and last cement the bottom end cap (the one with the cone glued in the middle).
Wait at least another 24 hr before doing anything else.

[Escher]

the next consideration was the sand. I opted for some glass crystal the size of course sand, but finer than aquarium gravel. I also thought it was lighter than sand and would move more easily.
I had read to fill the pipe by one third; I started with a some small gravel from a working tank (I thought I would add some nitrified material!) and topped the rest with the green glass crystal. The fun thing was putting the sand through the outlet hole
I had also covered the pvc pipe with some thing foam and some sarking to reduce thermal loss.

[Escher]

Testing time. After a minor set back with a smll leak from the top end cap (too weak - I reinforced by glueing another pvc sheet on top. But it would need a screw connectors with sealed internally with a nut) I finally got the thing working. Well sort of. THe sand wouldn't move despite a 6000L pump from the sump. I angled the pipe almost flat and it got going. Some sand was blown into the tank but it was to be expected.
Looking through my windows now the was some sand movement but only upto half the middle windows. Water pressure was high though and there was quite a current in the tank. The discus would not like that much, so I reduced the flow through the inline tap before the fbf inlet. But the sand almost stopped moving.
I tried removing some crystal by laying again the pvc pipe (easier than disconnecting all the pipes again!). Things got worse: less sand movement (now up to the bottom of middle window) and water pressure still too high for discus. If I reduced the flow, there would be no sand movement. Also the inlet pipe somehow was dislodged form the middle (I thought the tip of the cone inside the pipe would have stopped any eccesive movement)
Out it went the whole lot!
So why it not work???
I have come with some possibilities (but feel free to add some more):
1. PVC pipe too tall = less pressure inside for sand to be swished around.
2. PVC pipe too wide = more difficult for the water to push up the sand.
3. Wrong type of sand.
4. Maybe just wrong type of filter for discus!!!

Hopefully this experience will help others from making similar mistakes and come up with a better design. I guess the concept is easy, but fine tuning is not so straightforward.
Put your thinking cap on!

[flukes]

Mate you didnt do a bad job, first mistake waaaaay too big. It should be not even the height of your tank.

Now the sand leaving out the outtake i first thought put a stocking over it, but then i though of other designs and i hadnt seen it done yet.

So that makes me think 2 things, either you put too much sand or the sand is too light. The design i saw the sand was still being swirled around but it kind of stayed towards the bottom making me think it was a heavier sand.

Dont give up mate i wanna see how this goes, Also how did you cement the perspex too the pvc? Ive heard the americans using weldon #40 but i havent been able to find suppilers of weldon in Australia.

Also where did you get your perspex from? I went to bunnings and the perspex they had which wasnt much was thin and you could wobble it like cardboard.

Try again with a smaller sized unit i think that the biggest problem.

[Escher]

Would you believe it? The perspex was part of ... an invitation card!!!! (Weird eh!!!) But it shouldn't be too difficult to find offcuts from a perspex and/or a signs shop.
I used the cement plumbers use; plenty of it. The blue part stays inside, so you don't see it.
My sand was also staying at the bottom most of the time, which is not what I expected to happen. I envisiged sand being blown all over the tube and expected having to adjust the water flow so that it did'd come out of the tube.
(I made it coming out of the tube on purpose to reduce the amount of sand in the tube, but as I said it only made thing worse)

[flukes]

You going to give it another shot? Ill be making one out of perspex soon, so i want to learn from how you go