Porkypuffer,
I think your lighting might be a bit too low. How large is your tank? Your mushrooms might survive under the lighting that you have, but they will not thrive. I had mushrooms under normal output fluos. They didn't do much, but when i changed to high output lights, I saw immediate improvements.
Although mushrooms are tollerant of 'not so perfect water', I feel that a nitrate reading of 50ppm is pushing it. Try bringing it down. I remember reading somewhere that 40 ppm is as high a mushroom would tollerate.
A combination of very low lighting and higher nitrates is not helpful in the long run. Bring down your nitrates and consider purchasing a high output fixture.