700 + Aquarium Build

This is my first post in this forum but I've been lurking around for quite a while now. I'm on my 10th week or so in my fishtank building and it's still far from getting done. Size is 8L 4W 3H. Here's some pic on the first 2 weekends of work.

I will be using ABS plastic sheets to seal the plywood. I bought 3 pcs of 1/16" 4X8 sheets at $30 each. It might be a little costly than using fiberglass or drylock considering that I still have to buy GOOP to seal the joins of the sheet. The advantage I see in using this is that they are flexible enough to be affected by the wood warps and bowing (I could be wrong though).

I cut the sheets and just glued them with contact cement to the plywood. Didn't really put that much glue on it just enough to hold it up, I guess. Then the corners, I seal them with goop. GOOP are runny so I have to tilt the fishtank to have the GOOP sit directly on the sheet joins. I leave it there for 3 days before I do another side. Used 1 box (12pcs) of goop for this.

I cut the sheets and just glued them with contact cement to the plywood. Didn't really put that much glue on it just enough to hold it up, I guess. Then the corners, I seal them with goop. GOOP are runny so I have to tilt the fishtank to have the GOOP sit directly on the sheet joins. I leave it there for 3 days before I do another side. Used 1 box (12pcs) of goop for this.

Third week on the project I decided to start on the stand. It will be about 3.2' high. I will only have less than a foot access on top of the fish tank from the ceiling but I thought puting the tank higher will give the tank a more striking look. I used pressure treated 4X4, 4X6 (on 4 corner legs) and ordinary 2X4. The 2X4 "X's" are in a standing up position so that I can put 2 of them per section of the stand.
Not really a good carpenter so craftmanship is not really that great. Good thing it's not going to be seen.

The front side legs are about 15" center and the back is 2' center. The low "X" there is going to be my access tot he sump Then I sandwhiched the the 4X4 legs with 1/2' plywood. Added another 4X4 on the inside of the tank after the plywood for the beams. I wanted the plywood to be 1 piece for added stability that's why the beam legs are out side the plywood.
Those beams are not nailed in yet.

I am going to try a few things in the filter system hopefully it will give me easy maintenance and lesser water change. One is using a settling tank. I really don't know if this will work or how effective it will be but the idea is to direct the water that comes out of the main fish tank to another tank and hopefully the dirt will settle at the bottom. The drain is at the bottom of the settling tank so when doing a WC the dirt comes out first. Dirt can be flushed out of the system with just a turn of a valve. Any body can comment on this idea?