thing about dwc if you weren't aware. see plants especially marijuana in a hydro setup tend to treat the nutrient rich water like a buffet line. only taking what they need. because of this the water can build up with toxic levels of elements and nutes the plant isn't using as much of (as other nutes in the water). leaving these nutes behind and having the grower person keep adding full nutes will only exasterbate the situation.
some recomend at full strength one feeding, then next feeding is plain ph'd water.
now other just do 1/3 the max nutes but feed it all the time. this seems to keep those toxins away.
but no matter how you slice it in a dwc with res you should really look into getting clearex and hydro guard. clearex is going to help get rid of some specific nute buildups that are common, ie salt, etc. and breaks them into forms that are no longer toxic (use once every 30 days or so.
hydroguard is just an anti algea that is safe for the plants. i forget how often to use this, as i ordered my first bottle yesterday and haven't recieved it.
hope this helps
l8r