So I got my tanks filled with saltwater, and now decided it was time to get some rock into the tanks and out of the brute cans that have been taking up part of my living room for the last few months. I also decided, that I would like to try to keep the rock up off the glass so that sand bed critters could better get under the big rocks to clean/keep the area aerobic.
I decided to go with some PVC frames, such as the simple U shape shown below. I figured the 1/2 inch interior diameter PVC would probably provide close to an inch gap under the rock and that would hopefully be sufficient.
In that picture the pipe at that time was just dry fitted to check if it would work and was the right size. I then glued up the U shape except for the two end caps. I then used some of my sand as filler to weight down the PVC. I read about some people drilling their PVC to avoid anaerobic areas, but I figured if the PVC was glued up like I would for my plumbing, it should be water tight and shouldn't become an anaerobic area in the pipe. Of course, the story I read about someone finding a six foot worm living in his PVC framework he had for his aquascape may also have encouraged me to keep it sealed.
Having read about flow currents (and tank inhabitants) moving sand, and desiring to not have PVC showing in my tank; I decided to "paint" most of the PVC structure with silicone and then coat it with some of the same sand I would be using in my tank, hoping to camouflage it somewhat should it become exposed.
Once it cured for a few hours (wasn't really worried about the silicone becoming water tight), went and tried it out in my tank.
As can be seen in the reflection, the bottom of the PVC is not coated. Now, to do this for the rest of my rocks, hmm, those cans may be in my living room yet for a while longer.