Probably not harmful then. Just unaesthetic.

ah that's wonderful to hear!

Just observe... if you see signs of trouble, a spray of Physan or similar fungicide/algicide product would likely clear it up, but better not to treat unless there's a problem.

Where i live in europe (belgium) I havent seen physan. Are there any alternatives that have the same result or any other fungicides that couod be available with the same way of working? I've never had tovlook into fungicides up until now

Maybe search for quaternary ammonium cation (or compound)... that's the class of products that its active ingredients belong to. I know that there are a lot of products that aren't available in the EU, but this one is benign enough that there might be available products of its type. (Quite harmless to people and animals, just keep it away from fish)

I don't know if it would be effective, but consider a few drops of dish soap in water in a spray bottle. Or Isopropyl alcohol 70% (also in a spray bottle). These work on bugs, maybe they work on the mold. Very generic. Doesn't cost much try, and no harm whether they succeed or not.

Hopefully you won’t need to take action. If the spots get bigger but stay small-ish and the plants are still happy and healthy, no action needed.

If you start seeing signs that the plants are declining or failing to grow when all conditions suggest they should (good light, temperatures, occasional fertilizer, etc.), maybe unpot one and check the roots to see what’s going on underneath.

Soap probably won’t do much for mold/algae but alcohol sprayed on the surface does help cut down on the visible growth. It’s not going to get the stuff deeper in the pot, but if surface fuzzies bother you, that’s the rout I’d pick.

The green speckles might be algae: light, humidity, and nutrition are the perfect culprit for them.

I don't think Sphagnum Moss is a good medium for beginners. It can be an orchid killer for several reasons. Orchids have roots that are fine tuned to work in the media where they've grown. If you change the media, the roots will inevitably die. This shouldn't be an issue if you repot during growth season, as the plant should grow new roots adapted to the new medium. But if you repot when the orchid is not growing new roots and on top of that you change the media, it's the perfect dead roots recipe.

I don't believe in letting the medium dry at all. It should stay consistently moist. Not wet. Loose "fluffy" Sphagnum tends to get soppy and if the roots are dying it will take forever to dry. I wouldn't soak Sphagnum even at the height of a heat wave in Los Angeles.

If you live in an extremely hot climate and repotted at the right time, you could get away with Sphagnum.

Otherwise, I think the only way to use it successfully is by packing it tightly and watering lightly, preferrably from below.

I tend to be with Mateo on this. Sphagnum is wonderful stuff, and it's anti-fungal as well, but it has it's issues.
Personally, unless it's a tiny plant, that cat would be in fine bark at my house. If it's anywhere near maturity, it would be in a medium bark. A well-drained substrate, most cats don't want to be that wet as long as moss is likely to retain it (in my experience).

it already was in sphagnum moss when i got it, so the rootd are adapted to it already. so no new media. and well, i've heard from plenty of people that if you us emoss it *should* be loose, to retain air pockets. if you compress it, you'll remove any air pockets and suffocate the roots. i only water just enough for it to stay moist for a few days and water as it approaches dryness.

---------- Post added at 11:13 AM ---------- Previous post was at 11:11 AM ----------

i know i'm going to rustle some feathers herew but i've seen people grow catts in moss as long as it doesnt stay wet for ages. i've recently eve' received an adult one potted in moss from within the eu and it's as healthy as could be. i tend to need to remy on moss anyway, as the watering jusy becomes hell in summer otherwise

You can grow almost everything in moss. Cattleyas do great, Phalaenopsis do great, Catasetinae do great... it's not about the medium alone, it's about everything working together. Watering frequency, technique, RH, temperature, air currents, type of pot... The air pocket thing is something that Miss Orchid Girl says on Youtube but assuming that fluffy moss will retain such air pockets without accounting for the water's surface tension is quite a random statement.

Regarding the fact that the plant came in moss and you repotted in moss means that the roots are already adapted is also questionable. As moss ages, the medium changes, and the fresh moss you add won't necessarily be equal to the old one. In fact, it most likely will be very different. But what is confusing is that you original post mentions you use bark, perlite, etc. So what is it, moss or a mix? And is the mix providing the same conditions as the mix the plant came in? Did you repot while it was growing new roots?

All of the above are important questions in order to find success. I recommend you soak in all info on First Rays LLC › Using Science & Logic to Advance Orchid Growing

---------- Post added at 02:42 AM ---------- Previous post was at 02:35 AM ----------

Mold only grows on decaying matter or extremely porous moist surfaces that may contain some sources of nutrition. So something is rotting, some cheap barks can be really old, funky, and decayed by the time you purchase them. Otherwise it's algae.