I use H202....about a quart per 15 gals....so 2 quarts or so for the 8 waterfarms after I've scrubbed everything with hot water and rinsed through all the #(!*$# medium thoroughly. Then I run the peroxide through the system for 2 days and empty it. If any gets missed the H202 becomes water anyway so no worries. For the tubing I got a pipe brush thing from Amazon.com and it works terrific to get the algae out.