Over this past weekend, I did something that needed to be done though I have never done it before. I swapped substrates with fish in the tank. Normally, I wouldn't risk wrecking a tank's water doing something like that. However, I wanted to try out the Versafilter that I constructed a few weeks ago. Based on its specs, I believed it would be up to the task of quickly clearing the water as I moved substrate in and out with my main tank filter turned off. I was correct.
I filled each of the Versafilter's four bottles with polyfill and capped the ends with cut-to-fit pond filter sponge, which has a nice density. At first, I tried to run the filter horizontally (completely in-line with the pump such that the connection utilized a single short length of hose). However, the filter assembly was more buoyant than I expected, which was surprising because I tested it and don't recall it being so buoyant. It really wanted to float, even when full of water. In any case, realizing that a horizontal implementation wasn't going to work, I had to modify it such that the filter assembly stood upright and the hose connections formed a "U" shape between the filter and the pump. Since this was being used in a 75g, I used the tank's top cross brace as a way to hold the assembly down with the help of a spring clamp.
This worked really well, with one exception. The pump I paired it with, as mentioned in the earlier post about the Versafilter, was a Sicce Synchra 3.5. I did this for a couple of reasons. One, I wanted a high flow rate because I wanted the water cleared relatively quickly. Second, the four bottle concept means, in theory, that you're splitting the intake power into fourths. Think of it like using your normal vacuum cleaner but having four hoses instead of one. To ensure that each bottle was drawing water at a good flow rate, a powerful pump was necessary. However, the 3.5 turned out to be a bit too much, based on the outflow. It didn't turn the tank into a whirlpool, but it was close. Nonetheless, the experiment worked and the fish, all 16 of them (cichlids, dithers, and a couple of catfish), seemed none worse for the wear.
The Cichlid Room Companion
Tropical Fish Hobbyist
American Cichlid Assoc.
African Cichlid Hub