Its a 30g tank. My first thought was why only a 10% water change per week? Up it to one 50% weekly until the levels are detectable by API kits (anything over 20ppm is too hard to determine in these kits). Easy problem to fix while trying to figure out the source of the problem. No skimmers and other equipment is needed since they only postpone water changes. This is the one huge benefit of owning your small 30g tank versus a 75g with sump - you get superior water quality by changing the water and not postponing it by use of equipment.