You say you've got a 55g already up and running? Take some filter media from that, or even gravel, or even a decoration, and put it in this tank or in the filter for this tank. You need beneficial bacteria bad, or you will experience some fish loss.
The likely reason for algae is the nitrite/ammonia spikes. Algae can consume nitrogen in these forms more efficiently than plants can.
Some other suggestions.....put more plants in! The #1 mistake I've noticed in new tanks is not enough plants, and you are no exception
Preferably, more stem plants that are fast growers. (like snoopfish said!)
Also yes, do more water changes. I'd say once per day, unless you get a good source of some established bacteria in there.
Might do DIY Co2, or use the Canister soon
by "use the canister", do you mean go pressurized?
I would say that with excel dosing and good survace movement, you shouldn't really need to go the co2 route. Just my opinion!