Try reading here at Hoya forum for \posts on my Hydro Kerrii, that should give you a good start.

So far, I haven't had any Hoyas that didn't grow well in semi-hydro. The biggest challenge is knowing when to add water unless you're using the pots specifically made for semi-hydro with the little meters that show you when to water:

If you use these, you just look at the water level indicator and add as needed. But these are expensive and cost prohibitive if you grow a lot of plants. On the other hand, if you use the net pots with your own cache pot, it's cheap enough, but it's a real pain to pull each pot up to check water levels, so it's crazy time-consuming to water a lot grown this way.

Denise in Omaha

Doug Chamberlain has a really good video on semi-hydro. Check out his video on youtube called Growing Hoyas the Semi-hydro way. It is very explanatory.