Yeah, I'm thinking that my next video will be on that issue.

My tubs are 400mm deep and the recent rainfall was about 40mm ..... so maybe equivalent to about a 10% water change. The medaka didn't seem to be affected but I made a 20% water change when I found the time. At my location there can be several days in the summer when rainfall exceeds, say, 200mm in 24 hours ..... often I'm away on vacation at that time ..... but when I return maybe a couple of weeks later all the tubs still have surviving medaka. Maybe the important point is that, if you keep medaka outdoors in conditions close to their natural environment, it's inevitable you will get losses due to rain, wind, temperature change, predators, etc compared with the controlled environment of an indoor aquarium. If you only have, say, 15 medaka, you worry about every potential problem ..... once you breed them and reach critical mass of, say, 150 medaka or whatever, then you accept that losses are part of the natural life cycle ..... or, at least, I do anyway.

I originally used water lettuce and anacharis ... but, for whatever reason, water lettuce doesn't seem to grow very well in my setup. So I was happy with anacharis which grows well as a semi-floating plant (and may be cheaper and grow better in your climate compared to salvinia) ..... it was only by chance I came across a small bit of salvinia and found it grows very well in my setup and climate as a truly floating plant ..... but anacharis is almost as good.