Besides the advice on that good thread Jim linked, your big Cicla sp. and snakeheads put out a lot of feces. Is your filtration really up to the job?
Are you rinsing the filter media in tank water whenever you do a partial water change? This keeps the water from getting too rich in dissolved organics, which will support a population bloom of microscopic plankton-- which have almost transparent tissues that scatter the light passing through water, making it look whitish and cloudy.
Some additives can cloud very hard water temporarily I'm told. But this is not that.
