It's October and time to think about bringing my fish in for the winter. The 250 gallon tank I've used the last 2 years is too small, it's time for something bigger.

I started off thinking I'd just buy an 8' show tank and modify it for use with a 3" drain. So I went ahead and set one up, got the drain working just fine and filled it with 400 gallons of water. All seemed well, so I added another 200 gallons. The next morning I came down and water on the floor, not a lot. OK, I drained the tank, resealed the 3" exit fitting, and filled it up again. Looked ok, that is until the next morning. Water again. That's it, I drained the tank and removed it. Now, the amount of water lost in 24 hours was probably about 1/2 gallon, not much, unless it's in your basement. Outdoors, this would have been no problem.

Several weeks have been lost, it's already November and cold outside, time to build. I really did like the circular shape on the show tank so I decided to try an octagon shaped tank to take advantage of the flow pattern. The design would be an eight sided tank measuring 8' outside at the parallel sides. Below is the final plan I decided to work towards.

Click on any of the images to view them larger

I made the 8 sections using 2x4s on 16" center. The framework was assembled using 3 1/2" decking screws. Four of the panels had square ends and four of them had ends at 45 degrees. The panels would be bolted at each of the 8 corners. In order to assure that the end 2x4s would align, I drilled and bolted the two end pieces together, then with a simple alignment guide on the floor, I attached the 45 degree piece to the panel. This would assure proper alignment. The inside was covered with 3/8 plywood screwed on. I then insulated the panels with R13 batting and used 1/4" plywood glued and nailed to the outside. 3/8" bolts were permanently set in the squared off panels (can be seen sticking out in photo below left) and the area between the 45 degree 2x4 and the 90 degree 2x4 at the end was left uncovered on the outside to facilitate tightening the nuts.

Squared of panels with bolts	Corner panels with open area to tighten nuts

With the panels completed, down to the basement and bolt them together. Everything fit as expected and assembly was accomplished in short order.

Next came the liner, I still hate all the folds in a liner, but, it was the only real choice. After filling and pulling and pushing and filling more and folding, I was satisfied with the fit of the liner. I stapled the top of the lining to the frame and trimmed the excess. Next came the drain pipe which is a 3" slotted pipe extending to the center of the tank and exiting at the bottom to a settlement tank. Through the wall was accomplished using Greg Bickal's Pipe Boot method. It works great and costs a couple of dollars. If you are not familiar with this, you can read about it here

Slotted 3" pipe in tank for pickup	Exit from tank to settlement

The settlement and bio-filter tanks are 54 gallons each and measure 27d x 27h, they were put on a 5" platform so that they would work with a water depth of 25-30" in the main tank. The settlement tank is fitted with an Answer 325 and the bio tank contains 75 liters of kaldness media agitated with 40lpm of air. From the bio tank, water is pumped back to the main tank with a 1300gph pump. The water exits a 1 1/2" pipe at the water level and parallel to one of the sides giving a nice circular flow. Ideally, the bio tank would have been 1 1/2" lower to account for the Answer.

Settlement tank with Answer 325	Air ring to drive kaldness
Bio with 75 liters kaldness

I added a top rail using 1x6 plastic decking board and stainless steel screws. This was easy stuff to work with and of course didn't need to be finished.

800 gallon tank up and running

Lighting is a homemade 330watt power compact fluorescent, 6 55watt 6700k bulbs. There is an additional 160 watts of normal overhead fluorescent lighting.

I also use a TrippLite APS512 as power backup. This is a nice unit, charges while in use and automatically switches to the batteries with loss of power. I currently have enough backup to run the two water pumps and three air pumps for about 2 hours.

330 watt power compact lighting, 6700k	TripLite 512 used for automated power backup

I needed top netting not only to keep the fish in, but also to keep our 2 cats out. I made a frame of 1/2" pvc and attached 1/4" netting. The entire front 3/4s can be raised as well as a 32" square hatch which I use when feeding, etc.

The entire project took me one week and I am pleased with the results. The main tank works well, with the drain picking up the waste very effectively. The settlement and Answer do the job for removing all the bigger stuff, i.e., > 150 microns. The kaldness has no problem keeping up with the bio requirement and I feed well. One downside has been that because the kaldness is essentially self cleaning by virture of the constant aggitation, sluffed off biofilm gets in the water column. A lot of this remains in the system as suspended solids which are too small for the Answer to clear. The consequence is less clarity than I would like. I will need to implement a post kaldness fine mechanical filter to correct the problem.

A couple of additional pictures

Exit into tank - 1300gph	Netted top with feeding hatch up

Closeup of corner connection & bolts	Some of the guys who call this home for the winter