How often should I change the water in my reservoir?

The longer a tank sits, the more the pH and EC wander, and warm standing water grows slime and bacteria. Weekly is safest for small tanks and young plants, two weeks is about the limit for a big, clean, cool reservoir. Top-ups between changes are fine, but top up with plain pH-adjusted water or half-strength feed, not the full mix, since plants usually drink more water than nutrients.

Keep the tank covered and dark. Water tanks and submersible pumps are the basics for a reservoir setup.