Well, most people like to use chaeto since it does a good job of using up the excess nutrients in your water, and definitely does not go as asexual such as grape caulerpa. For the caulerpa to NOT go asexual, you will need 24/7 constant lighting, so that would not be a good suggestion considering it's going in a fuge in your main tank, in which you can't keep the lights on 24/7.
However, you may want to save up your money and invest in the RO
system. I know it's a lot of money, but you can find cheap units locally or through ebay, and it is definitely one of the best pieces of equipment you could have for a SW
tank. There's a lot more than just phosphates in tap water that are harmful or nuisances to SW
tanks, and RO
units get rid of most, if not all of them. The only thing that the macro algae will lower are your nitrates and phosphates.. not to mention it takes time and you won't see any overnight changes in the levels of both. But regardless, it's definitely a good start so go with it, and it's definitely good that you are doing research. Research is key all the way around.