Sounds like you need more clean up crew that will work the sandbed here. Nassarius and Cerith snails and a Fighting Conch will help to keep the sand clean.
For the green bubble algae is it Grape Caulerpa or;
Valonia macrophysa - smaller clustered elongated bubbles
Boergesenia - clustered, though less dense in numbers and elongated bubble shapes
Ventricaria ventricosa - can get quite large (around and inch) and grows in clusters and in singles
Dictosphaeria ocellata - usually smaller grouping slimey looking bubbles, can be a lighter shade of green
Dictosphaeria cavernosa - encrusting like growth forms with pitted looking bubbles
Here is Grape Caulerpa
And here is Valonia.(Green bubble algae)
Depending on which you have will tell us more on what you need to do to get rid of it. Just be aware that with any algae it needs light and nutrients to thrive. Tell us how long your photoperiod is and what your feeding schedule and how many critters you are feeding is.
