JamesC said:If you dose traces (micros) then one of the components is iron that is complexed in a chelator like Iron-EDTA. This is done as free iron is very reactive and will react with many things in the water making it unavailable for the plants. UV breaks the Iron-EDTA bond freeing the iron.
A lot depends on your setup to how much UV affects iron deficiency. Size of UV makes a difference as well as flow rate through the UV unit. If you dose lots of traces daily then you are much less likely to see any problems. Also the traces you use makes a difference as different chelators are used. Some people don't have problems whilst others do. The recommendation is really only to use a UV if you have to otherwise it's best to leave it out.