Miltonia Spotting and Browning

[Rootsnleaves]

Hi,
This miltonia was purchased in February, and had healthy green leaves. Since then, brown spots started to appear from the tip and then travel down the leaf. In some cases the leaf has turned completely brown and dried out.

The plant is flowering and new leaves are appearing at the base, but the older leaves look terrible.

I grow under T5s and water every 4-6 days.

This is the second time this has happened to a Mintonia. I have looked through this discussion and at the Fungus and Bacteria link, but am not sure exactly what i am dealing with.

Help from some more experienced growers, please?