No water flow from floor inlets

[SKP Fairways]

I recently discovered that following previous pipeline repair work more than 1 year ago (when the floor inlets were all closed), that the worker failed to reopen them all after the repair was completed. Having now personally reopened them all only 8 from 16 have water flow through them. I checked this out as the pool was getting dirty very quickly and small black algae spots were everywhere. The floor has been thoroughly vacuumed and brushed removing all the algae. However despite all the cleaning and 3 weeks of running with them open I still have no air flow through 8. When I opened one inlet a lot of debris came out but this was not the case for any of the others. Could there be a blockage somewhere, if so how do I clear it? What can I do?