Koi Rescue
Phoenix Arizona

Backflush Air Distributor

The idea of pulling all of the rocks out of the filter and cleaning them by hand really sounds like a lot of work, that I probably won't do. So I opted to look into the air bubble backflush cleaning method. This is where air is blown into the bottom of the biofilter and that bubbles all the muck to the top, so it can be siphoned off.

Most of the websites on the net seem to go with a spa blower, the air compressor unit out of a hot tub / jacuzzi. I looked around and the cheapest one I could find was about $110. I thought about trying to get a dead hot tub off craigslist.org for free and pull the unit out of that, but it seemed like a lot of work.

My next thought was to make a nozzle for my leaf blower. I have a fairly powerfull leave blower and tried an experiment -- I duct taped a 1.5" piece of PVC pipe to it and stuck the far end into my pool, and the blower was able to make bubbles at the bottom of the pool. So for a while I was planning on using that right up till I got the idea of....

Using my shop vac (blower end) as the air blower ! I have a small "stinger" shop vac, it is a wet / dry vac that has both a suck and a blow hole to hookup the hose. Just happens that the hose fits perfectly over a 3/4" piece of PVC pipe. So here comes the big question - does it have enough pressure to blow bubbles under a couple of feet of water?

I quickly put together this test rig from spare PVC parts, didn't even glue them together, just pushed the slip fittings together.

The bottom arms have 1/16" holes up and down the sides. I thought about doing the calculations on exactly how many holes I would need, but then figured that I could always just drill more if the vac sounded like it was under too much of a pressure load.

Starting at the top with the vac on, it bubbled away just fine.

Then as I would push the aerator down into the pool, the bubbles would start to decrease a little bit. Then about 3' down in the water, the bubble action seriously decreased. Good enough for me though, my filter is only going to be a couple of feet deep.