do siamese fighting fish change colorsfrozen food like blood worms also are good. WaterRainwaterRainwater is usually used. Some people use it successfully, but not all rainwater is safe for fish. Rain, as it falls from the sky in Rural areas is commonly good water. When it comes into contact with the roof and gutters and then stays in the rainwater tank with any leaves etc which have washed in, it picks up contaminants. Some of these are harmless, but others can kill fish.