Looking at your sump, it looks like it is designed as a refugium. You will need create a path for the water to convert it to a wet dry filter (which I assume is what you would like to do) you will need to create a path for the water to flow through the chambers. Note that all of this advice is user beware. I am currently working on my sump setup and all of my comments are based on what I have read. I have not tried any of them. I will end up repeating myself on some items so please bear with me.
I'm going to make some assumptions that you will need to correct if they are wrong:
1) You want this thing to operate as a wet dry filter (not your only option)
2) the purpose of the sand is to reduce nitrate and nothing else
3) Any modifications you make will be done with an eye towards being able to reverse them if later desired
A couple of things of note:
1) Its currently desined as a fuge
2) you are trying to use it as a combined fuge, wet dry type thing
3) you have a bubble wall.
The first step is to seperate out functions:
1) find another way to deal with nitrates
2) Use the sump for biofiltration only
Nitrates first. You have two options. i'm not going to go into deatail on either, You will have to look them up:
1) you can build an algy scrubber.
2) how much space is left in your stand? If you have enough space, you can place a second container next to the sump and use it as a remote deep sand bed (RDSB). Many folks use a bucket for this. The idea is to pick up a 5 gallon container and fit it with two bulkheads (one inlet and one outlet) or just an outlet and have the water enter from the top. fill the container with the pool sand and run a couple of inches of water over it. It is important that the flow is fast enough, or that the water is prefiltered, to prevent buildup and clumping of the sand. Make sure that it drains faster than you are pouring water into it, or it may overflow. If you google this you will get plent of ideas as to how to implement.
Second step is to redesine your fuge. You will want to turn the three section into a single section. you can drill the wall neer the bottom on all three sections, excluding the wall that does not go all the way to the bottom. Place PVC pipes with a couple of wholes drilled in the secions (excluding the pump secition) and place eggcrate on top of them. This will create an area below the bioballs for the water to flow. You can than add a drip plate (possibly pegboard) covering the three sections. Place filter media on top of the pegboard. Fill the three sections with the bioballs. The water will flow over the dripplate, and trip into the three sections. The water will now flow through the bioballs, through the wholse you cut, under the bubble reducer wall, and into the pump chamber. The water level in the sump will be the level necesary for the pump to run. If you decide to revert, you would take the wholes you cut out (use a whole saw) place them back into the wholes, and weld them in place. You then cover them with a thin sheet of accrilic and weld it in place (to make everything water tight).
Hopefully someone who knows more will chime in and let us know if this idea will work.
Best of luck. If you follow the forum you will notice I'm asking lots of questions, so my advice is the advice of a nubie. get confermation from someone else prior to trying my idea. I may be missing something.
