Fungicide in the UK

[MiniatureOrchids]

I've got a bit of grey fungus/mold on the roots of a phalaenopsis, and I want to treat it with a fungicide. However, whilst everyone mentions "use a fungicide" all over the place when talking about orchids, it's nigh-impossible to find out which ones are suitable and in what dosage.

I can't use cinnamon, as the fungus is on the roots, and the cinnamon will dessicate the roots and cause more trouble, probably.

A lot of people mention Physan 20, but it's no longer available for sale in the UK.

I've heard some people say any fungicide suitable for roses is suitable for orchids - is that correct? If I get something like Bayer Fungus Fighter in it's pre-mixed spray form, can I use that - and can I use it directly, or do I need to dilute it?

Recommendations please of brands and exact mix strength would be really appreciated.