SW to FW tank

[fishfreak]

So a friend of mine gave me a around 45g tank, he used it for saltwater, and now I want to make it into a freshwater discus tank. On the bottom of the tank it has 4 holes through the aquarium and has bulkheads in them and in the middle of the tank it has 2 bulkheads. On the top it has a overflow box with a bulkhead in it. I have a question if I block the 2 middle bulkheads on the bottom and leave the left and right bulkheads for the water to go down into the sump that im going to build, and block the 2 bulkheads in the middle and leave the top bulkhead in the overflow box so that the water from the sump goes to the overflow box and into my tank is that going be okay? And another question what can I use to block those 4 bulkheads that im not going to use?

[trbkrb]

No, that plumbing design is not OK. It is just the opposite of regular overflow plumbing. The overflow takes the water down to the sump and then a separate line returns it to the tank. The overflow is there to prevent the entire tank from draining.

Are the plastic bulkheads intact with the rubber gaskets? Are they threaded on the inside? If so, you can just get a few PVC plugs at Home Depot, and with some teflon tape or teflon putty on the threads, screw them into the bulkheads to seal them up. Or you can completely remove the bulkheads and use pieces of glass siliconed to the bottom to seal the holes. Use 100% silicone, no mold inhibitors, to make sure it is safe for fish.

As for using the holes for plumbing, you have to make sure the plumbing from the bottom goes to the top of the tank to make sure it won't accidentally drain the tank if the power goes out or something. I'm sure the 4 holes are for a closed loop system where the water is pumped from one or two of the holes and out the others back into the tank. There is little chance of draining the tank with a standard closed loop unless the plumbing breaks.

Pictures would be great if you can take some. But if you only have one hole behind the overflow, you will have to make sure that it is always clear or you risk an overflow from the tank. And for the water return, you can use one of the holes, but you need the plumbing to extend above the waterline and then back down so you can have a siphon break, also to prevent the tank from draining too much if the power goes out. Most people just have the return going over the back of the tank for this.

What I would do if you don't mind having PVC pipes in the tank. Plumb one of the holes for your return and do a siphon break and put locline or something on the end to direct the water flow. Use another one of the holes for an emergency drain to the sump and have the PVC pipe end just below the top trim, but above the regular water line. This will only be used if the main drain behind the overflow is blocked or partly clogged. Then you can block off the other two holes. But if you don't want PVC in the tank, then block off all 4 holes and do the return over the back and make sure you clean out the overflow drain frequently.

Good luck!

[40GallonsOfDoom]

The word bulkhead and its plural bulkheads has now been used 13 times on this thread.