just rinse it out well whatevr you use. could be bleach doesn't matter as long as you rinse it out properly.
empty, clean, refill.
if it's already got a biofilm or cloudyAF no safe amount of chlorine or similar will help, lol. the way i run my rez, i do a 75% refill every 3 days. It never sets overnight less than 1/2 full. Refreshing the water can delay need for cleaning, but it has to be done at some point. Just time it with a low point. Fertilizer should be cheap and of no concern to throw out even a few gallons. dump it outside somewhere, it'll get used.
if that is some sort of 'safe' additive, you need to use it before there's a problem. Probably only delays the inevitable.