Re: fresh water tank ?
The Chlorine in the tank is slowly depleted over time. As long as there is ANY Chlorine in the water nothing will grow.
Go to any place that sells pool supplies and buy just the
OTO Test Bottle.
(OrthoTOlidene)
Occasionally, run the water for 10-15 seconds and then collect about a 1/4 ounce of water in a small glass.
Add 3 drops of the OTO to the water. If it turns ANY shade of Yellow/Orange. The Tank Water still has Chlorine in it.
If it is clear, flush the tank with fresh water or add some Chlorine Bleach at the 1oz/24gal rate.
(~15 Parts per Million)
Note:
15ppm is a high level compared to the ~4ppm delivered by municipal water systems.
The concentration will be lower and may be zero a few hour later if any thing had started growing in the tank.
After any Chlorine addition, A retest a few hour later is indicated.