"*muffin*" writes:

(yes I know some of you don't believe in them...........vbg......... so
ignore)

I believe I believe!!

do any of you KNOW where there is info on how you can tell if the UV filter
is working?
mine is in its 2nd season, has been running a month & the water is still
nasty green.

If the bulb is glowing and this happens I replace the bulb.

the lights are still glowing on the thing ( its by pondmaster).

Make sure about what the lights show, just AC power or the bulb itself
glowing. I replace ballasts about twice as often as bulbs, maybe 5 years
for bulbs and 2-3 for ballasts (I should spend more money and get industrial
strength ballasts).

Anyway, ballast or starter going bad will give a dark bulb (so will broken
bulb filament). Bulb glowing and algae is bad bulb if other things haven't
changed (eg fish load, sun, pump)

You can test ballast/starter with a spare non-uv bulb (cheap). Or keep a
spare uv bulb around. I either see the filament broken in the bulb or
(once) the end wire broke off the bulb and I couldn't solder it back.

HTH