The reason you test 0 is because the algae is using it all up. What it sounds like she needs to do is a massive invasion on her tank and a 50% water change over the course of a week. You stated earlier that all she has left is a clam, if so then if she can purchase a 10 gallon tank and a clip on desk light and throw a 50/50 PC bulb in it to help it survive along with all the QT equipment.
This will allow her to take maximum steps in fixing this problem. Once thats done. Kill the lights. Don't turn them back on until you are sure its under control. Next step is to attack the glass. Pretty easy to do. Turn off all water flow then take some filter floss and start rubbing the glass bottom upward motion removing the algae that you wipe off. Take the floss and rinse it in 20 secs of the hottest water you can stand. Then repeat until glass is clean.
Next step, sand, move all rocks and such to one side of the tank and deep vac the sand bed it should pull a lot of the algae out. This step will also remove about 20% of the water by the time your done, depending on how much algae and how deep the sand is. Once the one side is all nice and good move everything over to the other side and do the same. Sand bed should be good now.
Next, take about 5 gallons of the water and a soft toothbrush and piece by piece pull the rock out and pull the hair algae and scrub the other algaes off the rock as best as you can. Keep the rock submerged in a bucket or some type of container the entire time. Keep the cleaned separate from the old rock. Should be easy if rock is still stocked to one side of the tank.
Now that you have taken extensive steps to bring the algae down, you can re aquascape the rock and place everything in. While you tank may be able to support life I would suggest against adding anything outside of snails, hermits & maybe a shrimp or two. You need algae eating livestock that will remain in the tank for the long term of the tank.
Still keep the lights out, these critters don't need light to eat. Keep an eye on the tank and over the next few weeks monitor parameters. You may in the beginning after cleaning have a spike in nitrates since you cleaned the sandbed so much.
This procedure I suggest only if the tank is completely taken over by algae not spots here and there. Similar to this even if its not this extreme anything close.
Had a friend use this procedure just 3 weeks ago when he was taken over by algae. Only difference is he had no fish but corals. Only difference was he moved all coral to one side on egg crate and the rocks to the other and used a black piece of plastic to block the light from reaching the rocks and sand. With 1/2 of his PCs on just the coral side.
Virtually no algae in the tank now, id say 2/3 more weeks and he will be able to rebuild his reef.
