(Accidentally sat on this post for a couple days....somehow it become "lost in the tabs"....hope it may still help.)
If the coral is already stressed from having old lights and has lost color and polyp extension due to depressed alkalinity (have you confirmed this with a test kit yet? what is the actual number?) I would not recommend moving it to a new tank on top of that.
I would say to just do your water changes and/or doses to make the alkalinity better in the tank where he is and get those new bulbs in place ASAP. (If alkalinity is too bad, don't correct it all at once, or drip it very slowly if you do.)
Also, just for the record here's the total cost on a doser:
- Aqua Lifter 3 gph pump: $15
- Airline valve (6 pack): $7
- Timer: $8
So, for $30 (+/-) and a little bit of bother, you're automated.
FYI, I used all Drs Foster & Smith parts and prices for the three main parts for universal accessibility. If you're willing to shop around you can do better on some components (like the valves - Top Fin are my favorite, which most Pet Smarts seem to carry, and of course you don't need a 6-pack either) and prices (see AquariumGuys.com for Aqua Lifters) - especially if you're not afraid to shop eBay and do something a little more DIY.
Good luck - hopefully there's minimal/no scarring after the Rainbow recovers!
-Matt
P.S. At home I'm currently running one Aqua Lifter and one eBay-sourced DIY peristaltic pump on my ReefKeeper Light. I like the setup and both pumps are very inexpensive.
P.P.S. Make sure your alkalinity and Ca test kits are up to snuff when you start automating - you're still going to want to keep a close eye on alkalinity and Ca too for unexpected changes.