Swirl Tank

So the two hundred plus or minus koi fish have been rescued from certain death from abandonment at my neighbors pond and are residing comfortably in my talapia tank. Now I've got to put it in gear and get the system plumbed and running to keep their world habitable. Although they have been living in a stagnant, algae filled, slime pool without air for the past year. So I've probably got some time.

An inexpensive swirl tank 

 I started off by moving about four hundred gallons of their water with them to start my thousand gallon tank off with some good bacteria. I'll fix the algae problem later. To build a good swirl tank on the cheap I started with with a Rubbermaid Brute 44 gallon trash can. Into that I put a 1 1/2" thru hull fitting at the bottom of the can for the clean out valve. The swirl tank needs a cone shaped bottom to direct the solid waste down to the clean out. I made my cone from an old dome style trash can lid. I cut off the lid handles that were sticking out then made a cut from the outer edge to the center. This let me pull the two cut edges past each other to make a cone shape. This cone is then put inside the can at the bottom and let to expand out until it fits snug to the sides. It will still be overlapped and cone shaped. I used a sharpie marker to mark the cut edge. Then remove it from the can.

I rebent the lid until the cut edge lines up with the sharpie mark, then run in a couple of 1/2" sheet metal screws thru the lip from the outside towards the inside to hold it in shape. This way the point end of the screw won't poke into the can wall.

I cut and glued up a piece of 1 1/2" pipe and 90 degree fitting and put it in the through hull fitting at the bottom of the can so that the 90 lands in the center. I cut that 90 so that the end that is pointed up is only a quarter inch long. The part that I cut off I used to scribe the center off the cone that I made earlier. This is then cut out with a saber saw so that when the cone is put back in the can it will fit snugly over the PVC 90.

I caulked around the PVC 90 and the outside edge of the cone with 3M 5200 marine caulk. This is a tuff caulk that will hold it in place without screwing through the can wall. I also used it on all the through hull fittings.

On the outside of the can I reduced my clean out down to1" pipe and put a butterfly valve inline. I then put a 1 1/2" through hull fitting through my fish tank a the finished water level height that I want, then lined up that fitting with my swirl tank on the outside.

A matching 1 1/2" through hull fitting was installed into the tank and PVC pipe was press fitted in to connect the fish and swirl tanks. I only press fit these as there is so little head pressure that high up in the tank. It also makes it easier if you have to move it later. This pipe gets a 90 on the inside and a short piece of pipe kicked at an angle to get the swirl going. The last fitting goes in a couple of inches lower than the inflow line and a piece of pipe is stubbed up to establish the tank water level. This is the outflow line that goes back to the sump tank. So now you have an inflow an outflow and a clean out line. The solids come in from the fish tank, swirl around, settle to the bottom, and are cleaned out as needed. The clean water rises to the out flow and exits to the sump.