T5HO in T5 Fixture
 

I have a POS Coralife T5 strip that has 2x20w T5 bulbs, 1x10k, 1xActinic. Can I replace these 2 bulbs with one 39w T5HO actinic bulb, would the ballast fire and light the HO bulb ok ?

it will over drive the light by a bit IMO and IME i dont like to over drive lights something about Nature and murphy's law has something to do with it.. it ma work for that 1 watt its worth trying out. so you are wanting to take out 2 bulbs and replace it with 1 I would just buy a new fixture and run 2 again.

I don't know why Coralife even makes these with reg T5 ballasts ...
Heh, whats even worse is that I happen to have one :(