Well, your choices are limited. Caridina japonica always come to mind, but it will be eaten by the puffer. Some members in the Gobiidae family like knight gobies nibble on some green algae, but wont make a dent in the algae as a whole (and will most likely eat the bumble bee gobies). Molly's graze on algae but wont control it in a brackish tank. Yoy could try some different livebearers like platy's or guppies but are not as effecient algae eaters as Molly's. Jordanella floridae is an algae beast, but it is a semi-tropical species and wont tolerate tempatures over 75 degrees. You livestock options are limited but the best way to rid a tank of algae is to plant it. Low salinties like yours allows a variety of flora, which if well maintained will rid your tank of almost all algae. It would not be hard to plant this tank, just invest in some appropriate lighting and possibly a carbon dioxide system (or a wallet friendly DIY version) and youve got a planted tank!
So all in all with your current selection of fish and current salinty, you are pretty much limited to Molly's or different livebearers or planting to rid/control your tank of algae.
