on my 50 gallon tank 36 in long. i went with 250 hqi, blue wave 3 ballast with reef optix III. with 14k Phoenix. the set up was great. (also heard it was one of the best lighting) good thing also that i thought of was if i ever need to upgrade i have gotten the light out of the way. i could grow everything like sps, lps, soft. anemone and it would be fine. gotton may great comments of the fixture and how it shimmers in my tank.
i have to down grade because i have 100 gallon running 2 250watt also plus everything in tank almost 1000 watt for about 4-6 hour is too much. so i am in the process of selling this set up.
i would suggest if you do get the 250 watt you could use it for the 29 gallon but you could also upgrade you tank to a 50 or 55 36L and it would also be fine. for one tank it would be great for a show tank. (in my case just have too much). i am also guessing that your 29 gallon heater, pump, power head and stuff would run about same watts as a 36l 50 gallon. i choose also a bigger tank because of stablilty of water conditions, and larger volume of water is harder to heat up. just my thoughts
klam114