sand bed critter question

I have a dsb and I'm getting ready to replenish my stock of sand critters.
what I would like to know from 'yous guys' is, what are your recommendations
for a dsb... what kind of critters and how many... I have:

125g tank with about 4" bed in front sloping up to 6" in rear
95g refugium with about 4" bed that measures 30"X24"

Occupants in tank:
1 purple tang
1 coral beauty
1 bi-color blenny
1 lawnmower blenny
2 percula clown fish (pair)
4 cardinals
2 sand sifter starfish
1 large red brittle star
2 xenia
numerous corals

**problems**
I'm getting a lot of bubble algae
there are a couple of areas in my dsb that almost look like the sand is
starting to form a top layer that is hard.. about 1/8" thick with a green
tint to it

would I be better off just sticking to a package deal at an online supply?

any help would be greatly appreciated

thank you for your input and taking the time to read this

SNC