IWS DWC maintenance

I'm doing my first tester grow with this system and working out some kinks and I've hit a roadblock. I began some blue cheese and everything was going great, fast growth and the like. I'm not into day 35 of flower and the plants seem to be slightly stressed and the growth and bud formation has slowed down somewhat and In the buckets themselves there seems to be a white-ish slimy residue building up around the bottom of the buckets.

Tomorrow I intend to put in a complete fresh water change but since all the buckets are linked up via piping and the buckets don't drain untill completely empty I'm wondering how to best go about cleaning the buckets. Bearing in mind its not possible to detach any bucket separately to clean.

In general I'm just looking for some options that I may have to keep these systems clean.

put the plants/lids in separate buckets then clean out all the buckets, air stones and res. wash it through a couple of times with fresh water then put them back.

I would make sure you are getting ample amounts of air into them buckets.. The bigger the plants get, the more oxygen requirements. I had similar problems and now i use a 280 watt commercial air pump and run without air stones.. Perfection all the way!