Pleurothallis with brown leaf tips :(

[m_ms09]

I have had a pleurothallis alveolata for about a year now and I am keeping it in a large orchid tank set up that I use to grown my humidity-loving cloud forest orchids. The tank stays at about 80-95% humidity and has good airflow with a computer fan that blows mist from a mister towards the orchids and out an opening at the other end of the tank.

Yet, my Pleurothallis is constantly browning at the tips of the leaves - even new leaves a few weeks after they have just developed!

Anyone know what I may be doing obviously wrong?

It's potted in a 3.5" plastic pot in sphagnum.

Thanks!