Figure out what the algae is feeding on, if the person caring for the tank overfed then that could be a cause, maybe there was a lack of water changes, etc.
Many causes to algae such as the use of tap water, overstocking.
Bubble algae is actually one of the harder algae species to remove, they do not need too much nutrients in the tank to survive, many people have had success with emerald crabs. Try not to pop them though ( I know emerald crabs do ), popping them by hand can cause them to spread, right now, figure out the root of the problem, siphon as much out, without popping, as you can, and start wet skimming.
BTW testing is useless, the algae will consume the nutrients before you can test for it, meaning nitrate and phosphate.