Well gang, it's been awhile.
I was talking with a biologist who works at an Ohio zoo. We were rambling on about all kinds of stuff when he happened to mention that he had built some tanks from PVC also, but not as large as mine. He said he put the angle stock on the outside of the tank instead of the inside. His thought was that if there was a leak, there would only be one seam to repair instead of two (one seam on each edge of the angle stock when it is inside the tank). I thought that would be something to try and also thought a bead of silicone could be run around the inside seams to seal them. I asked around and spoke with quite a few people about it, then decided to go ahead with it on one tank to see how it went.
The building process was much easier. I didn't have to make sure that all of the glue joints between the angle and the tank wall had a continuous stream of glue, the joints between the walls were much easier to align straight and square, the angle could be set on the workbench and the weight of the wall would hold it in place while the glue dried to ensure a good bond. It just seemed like a better and more convenient process all the way around. I received some advice to sand the joints a little to allow the silicone to bite into the pvc and form a better seal, so I did that. Well, that tank ended up with more leaks and gave me more trouble than the first four tanks combined. I ended up digging out all of the silicone and laying a fillet of glue in a double layer on the inside seams to get it all sealed up. The sixth tank was being constructed at the same time, so I went straight to the double layer of glue and this tank was, amazingly, leak free.
Now I am considering trying my hand at heat welding the inside seams. Always changing, always trying something new.
I also revisited the idea of plumbing the live rock vat to surface overflow into a separate vessel before getting pumped up to the skimmers. The first time the vat was plumbed to overflow surface water into the cut barrel, there was only two of the four intake pipes overflowing into the barrel. There was one pump from the cut barrel feeding into two of the skimmers. The other two skimmers remained plumbed from a second pump which drew from the original submerged intakes. It was very difficult to maintain a consistent water level in the cut barrel. The wild fluctuations caused either overflowing of the barrel or cavitation of the pump. Both conditions put the pump in jeopardy by either getting wet or running dry. My recent thoughts were with the two pumps running, but only one plumbed as an overflow return, there was some kind of imbalance created with the second pump returning water that wasn't in the overflow loop. It really shouldn't have been any different than having a tank with an overflow to a sump and a return, plus including a second pump on an open or closed loop that is plumbed with it's intake from the tank and returning into the tank, but it was different somehow. There was just something in my mind that kept telling me it would work if I tried it again with all four intakes overflowing into the cut barrel, then using only one return pump to feed all four skimmers. This also had the benefit of eliminating the electricity usage of one pump, and lowering expenses is always a good thing. The vat was plumbed this way on Tuesday evening (10-25-05) and there have been no issues thus far. (The flexible tubing that is hanging from the vat along side the cut barrel is not part of the system, it is the hose I use to run around and top off the tanks. There is a hole drilled into the vat which makes a convenient place to hang the hose.)
Since the fifth tank is now available, I pulled the Sarcophyton elegans from quarantine. It had only been about thirty days, but it was sloughing mucous pretty frequently and forcing me to do nearly 100% water changes every couple of days. I figured it would be better to get it into a larger volume of water, plus it is the first specimen in the tank, so technically, it still is in quarantine.
Just a beautiful creature. Can't hardly wait to slash it into pieces.