GL is right, cyano.
It looks like an algea but it is actually a bacteria so yes your local shop is right and has given you good advise
As has been mentions, try and syphon off some if you can, increase the circulation in the tank as cyano is also an indication that the flow is low. Cyano hates higher water flows as it cannot get a grip so easily.
Im afraid there is no real fast easy or quick way to get rid ot if. Its part of the natural maturing process of the tank. Some times it can dissapear in weeks, others it can take months
Finding a cleanup crew to eat it is hard, most wont touch it so if your hermits are eating it then you are doing very well indeed.
What you must also try and discover is why its appearing. Cyano is eating something.. nutrient are high i would guess. I would tests for phosphates and nitrates in the tank.
Make sure you take water from as close to the cyano as possible, you will be astounded in the difference in phosphate levels in here when compared ot the open areas of your tank.
Once you have reduced the amounts of nutrients in the tank then the cyano will die off.
In the early setup you get cyano bloom because of the silicates in the sand etc. but once this is used up the cyano dissapears. Of course, if the tank starts to get high nutrients then the cyano will never go.