UV light can be a great addition to the tank . not only it destroy the free swimming parasite which can cause ich , it also destroy the spores of the algae . should be able to see a drop in algae growth .
take note of the flow rate through the UV as if it is too fast , it might not be as effective as it can be .
with that if ur tank is small and u are not using chiller , u might see a small increment in temp as it is PLC afterall.