Phragmipedium besseae leaves turns red
 

This is my first Phragmipedium and i don't really know if it's quite normal or if it's a disease.
Perhaps pictures can be more helpful

http://i21.photobucket.com/albums/b2...s/SAM_0494.jpg

http://i21.photobucket.com/albums/b2...s/SAM_0495.jpg

http://i21.photobucket.com/albums/b2...s/SAM_0497.jpg

and a new growth with some brown areas

http://i21.photobucket.com/albums/b2...s/SAM_0496.jpg

The medium is made with peat, perlite, bark, charcoal, expanded clay and lava rocks. Substrate always damp.

I'm no expert, but that looks like a really bad case of nutrient deficiency. That could mean you're not feeding enough, or that you're not feeding the nutrients in proper proportions, or that the mix you're using doesn't support the plant's proper uptake of certain key nutrients.

If I had to take a guess, I'd say it's got a magnesium deficiency, but don't take that as being the case. Can you describe how often and at what rate you fertilize? What brand(s)?

How long has it been since the plant was repotted?

To me it looks very over-potted as well as whatever is going on with the reddish pigment.

I suspected that it was a kind of deficiency...I have bought the plant bare root in September 2012 and immediately repotted.
As fertilizer I use Scott's Peters 20-20-20 half rate (0,5 grams/liter) each 10-15 days.

Definitely needs something in the way of nutrition and even for a Phrag that is overpotted.

Ok first step is repotting. Now it's in a 18 cm plastic post, I will repot it in a 12 cm pot.

Any suggestion about the kind of nutrition deficiency?

I would just give it a balanced fertiliser each time you water at the recommended dose for orchids. These should grow fairly quickly and like moisture so it should recover. I haven't seen a deficiency quite like this so I am not sure what else I can recommend. However a fertiliser that 'has the lot' should help. It will also be good to see how well the roots are developing which might give an indicator.

I'm not so good with phrags but how is the hardness of your water? Are you using rain water or something with low TDS? It looks like general stress response.

Actually I think you have a good point. In Australia is very good and our water doesn't need treatment. That would explain why we don't see this issue from what I've seen anyway. If the water is high in minerals maybe this is a normal reaction for the plant and you need to treat your water. That would also make sense.

Phrag Besseae is one of the more sensitive phrags to water quality, and most of them are more sensitive than other orchids.

They can also get brown tips from over fertilisation, through I've seen them go more brown and die back, than red, when that's been the cause. If I give my hybrid of Besseae the same strength fertiliser as I give my phals it will start browning on the tips of the leaves. I give it about half the strength I give others, and always use rain water.