On August 19th at DCP we began cleaning the IBCs, which we use as fish tanks, before we introduce new fish in the next two weeks. In order to clean the organic matter harboring anaerobic bacteria on the bottom of the tanks we used the siphoning method that Ojan suggested. Siphoning refers to a U-shaped tube that moves a liquid to flow uphill above the surface of the liquid using differences in atmospheric pressure and thus allowing the liquid to drain on the other end of the tube at a lower or intermediate water level.
(Ian, Yiran, and Colin siphoning the fish tanks)
The tools we used at first were a black flexible pipe, connected with a PVC, and a bucket to collect the siphoned water. Ojan taught us two ways to fill the pipe and PVC with water. At first Ian and I put the pipe and PVC under water, and Ian lifted up and down the two ends of pipe at the same height out of water at least three times. Every time there was supposed to have water coming out to show air being replaced by water. However, this method failed too many times and we learned another more efficient way which was to insert one end of the pipe into water and continue putting the rest of the pipe in until water came out from the other end. The next step after filling the pipe with water was discharging water to the bucket. Ian pinched the end of black pipe and drained the water to bucket while I held the PVC side and moved it around on the bottom of the IBC like a vacuum. This worked really well and the water began to look clearer.
On the next day, Colin used another approach to do the siphoning that widely opened my eyes. Colin connected the hose to the siphoning tube sitting in the first fish tank. First, he turned on the hose and let the water drain into the fish tank for a while to make sure the long pipe was filled up by water. Second, he turned off the hose and unscrewed the hose from the water pipe, thus creating an area of low pressure for the water in the fish tank to escape to. This then allowed us to put water in our dry creek bed as well continue with other garden chores while the fish tank was siphoned. However, a day later, Ian and I could not make this method work by ourselves without Colin; because we had forgotten the important step of unscrewing the hose from the water pipe.
Siphoning works really well not only for cleaning the bottom of the IBCs, but also for discharging the water from the whole first fish tank. Right now the first fish tank is totally empty and the algae on the side of the tank has become crispy and can be easily cleaned after time. For cleaning the smaller 55 gallon swirl filter I think shorter pipes and PVC are needed, or draining it entirely with the hose.
Yiran Song and Ian Earley