In my opinion, I am not sure the perlite is the best choice for semi hydro. The medium in s/h is key to this type of culture. The medium needs to provide good capillary action to keep the material uniformly moist and be inert so that it doesn't breakdown over time. But it should also provide lots of free air space.
The perlite in your photo shows very small pieces of perlite. If you are going to use perlite for semi-hydro you might consider using 3/4 or at the minimum 1/2 inch chunks. Also, perlite will breakdown over time and compress. This will limit air movement to the roots of your orchid.
There are many here in this community who use s/h and perhaps can offer alternatives to the perlite you have chosen. (You might even consider using small lava rock if that is available in your part of the world.)
Please others weigh-in. I have only three or four plants growing in this culture, so my experience with it is limited.