Making this has been a blast. But there has been a LOT of learning involved. Due to the size of this (27w x 17h x 11.5d) the buoyancy has been far greater than I anticipated. I have hallowed out the bottom 3" and have been filling it in with concrete in stages, to see how much weight I need to add to make it stay submerged.
I also bought an adjustable air pump, along with an adjustable manifold for fine tuning the flow, but I have a lip at the exit of the PVC
pipe that I am hoping the sand will hit and fall straight down. My plan was for this lip to allow me to tune the pump a little higher, without spraying all over the tank, which should give me a wider "sweet spot" for the flow. I have pool filtration sand at my house as I have a sand filter for my pool, and I have read several different places that this is the diameter sand you want (~1mm to 1.5mm).
Things that I have learned:
-Make your structure as hollow as possible. This minimizes the water you have to displace, and thus requiring less weight to sink it
-A hot knife is not necessary, but will make your job much cleaner
- Use cement, not concrete. Much more appealing, easier application, no rocks.
- The color of the cement dry will greatly change from the color it is applied at. I knew it would lighten up as it dried, but it was WAY lighter than I thought it would be.
- Thin your coats with water, and use twice as many coats as you think necessary.
Cost so far:
4x8 Sheet of Styrofoam:
10lb bag of cement:
1" diameter PVC pipe and elbows:
Tube of Silicone:
$1 - $20