The slower the gph
, the higher the "kill rate" for the UV
light. I would suggest anywhere from 100 to max 200 gph
for a 9 watt CF UV
. I personally run a CSL double helix 9 watt on a 58g tank with a Fluval 104 which pumps about 100 gph
. Keeping the same theory, I also run a 18 watt CSL UV
on a 90g with another Fluval 104, so you see that I keep my flow rate down for these small non- commercial UVs.
I've had more success with this type of setup than when I followed the manufacturers guidelines of 350 to 500 gph
on a 25 watt UV
that I used to run on the 90g. Hope this helps.