Have you changed the water within that month period? I ask this, as a few different approaches can work together to control or live with the surface scum. They are proteins and assorted compounds that a skimmer would normally remove, so installing a skimmer is one viable option but I realize this is a simple nano and that increases the complexity and the cost. Also, you can learn to live with some surface scum if it is reasonable and also partnered with recurring water changes. All my reef have surface scum, as they are unskimmed, and it doesn't hurt anything because I do not leave the compounds in suspension long enough to break down into materials that feed algae. I change the water and suck them out, only for them to build up again through the natural tank processes. Left in there and allowed to accumulate they break down into the elemental materials that feed algal blooms, but they do not necessarily cause them while they are in whole compound form (the actual scum--you won't be able to see the elemental material [Carbon, Nitrogen, Phos])
You can also take a paper towel and lay it on the surface, the compounds will stick to it and be removed to a large degree if you dab enough. Youwon't remove all the protein, but will do enough export to prevent a backup/system consequence. You can alter your feeding regimen to allow lesser feeding or feeding of a different type, I guarantee you a feeding regimen that is less meaty and more vegetative will not carry the asociated compound makeup--but then again there are nutritive factors to contend with. My tanks get a very small amount of introduced protein (a few frog pellets a week) to feed pods and a few higher-order shrimp. I give Dt's (vegetative) to help the fanworms and sponges, and this has found a happy medium in my sub-gallon reefs such that the amount of residue leftover is not enough to degrade in the system significantly. I also couple this with the water changes, careful stocking, and paper-towel technique. Employ one or more of these methods (get the skimmer if all else fails and you still want to keep your current fish bioload) and you should be able to get things under control.
Brandon M>
