All hermits tend to favor nassarius/cerith & io snail shells sadly, even though I've given my hermits plenty of spare shells
Red legs tend to be a bit lazy, you might wanna try some zebra legs & some turbo snails for the glass.
As a guide they say "roughly" 1 snail per gallon of water, but of course you can slowly build up to a point where you cleanup crew starts to win the battle with algae.
Over feeding/poor circulation are over causes for algae?
30gal tank, 20kgs Fiji + 4kgs Madagascan LR, bare bottom, 2 x Maxijets 900, AquaC Remora skimmer, 10W D&D UV using a spraybar on surface for return,Maxijet 600 + spraybar behind LR, Ecco 2234 running RowaPhos/GAC, 150w visitherm.
Custom Built lid; 2 x T5 megatwin (4x39W Aquablue+); 4 moonlights.
IKS with temp & PH probes, controlling lights,heat & cooling fans.
Percula Clown; Banggai Cardinal; Firefish; Mandarin
2 Cleaner Shrimps; 3 Peppermint Shrimps; 1 Blood Shrimp
1 Large Feather Duster; 1 Hard Tube Coco Worm; Yellow Cucumber.
6 Red Legged Hermits; 1 Green Emerald Crab; 16 Dwarf Blue Leg Hermits; 3 Zebra Hermits; 3 Popsock Hermits
22 Turbo/Astrae Snails; 20 IO Snails