Sorry, I was reading on my phone and didn't see that last part about your fixture. IMO, stringy tentacles or bubbled tentacles aren't necessarily a correlation between light levels. I haven't seen any great evidence to suggest why some bubble and some don't. I used to have one RBTA that at times would have half bubbled, and half stringy.
As far as bulb selection goes, I personally don't really like to use actinic T5 bulbs. There are bulbs (I don't have T5's anymore so forgive my forgetfulness) that will give the visual coloration of actinics, but with much higher par. I do really like the Fiji purple bulbs, they give quite a great POP.