How to keep a clean reservoir?

Hi. I have varying success with blumats and my biggest problem with the product is I can’t keep them functional for longer than a few weeks before something makes me tear down the whole setup and demands I restart from the beginning. This time it was my reservoir going stale: after sitting stagnant for 2 weeks the reservoir got a gross scummy pond water smells. I know there are products to keep the lines clean from bacteria, but assuming I don’t want to have to constantly pour products into my reservoir to keep this simple product functional, how do the rest of you keep your reservoir from going nasty? Should I really be changing the water regularly? Anyone found a solution to share?