Somethings causing your ammonia to reach between 0.25-0.50 and your Nitrates to maintain 20-40ppm. The Nitrates aren't the problem. It's the ammonia that you need to worry about. You need to get that down to zero. Those vials and charts look like API test kits which aren't too reliable in my opinion. Is it a marine test kit or standard? I think it's time to invest in a better test kit. SeaChem and Red Sea are good kits. You can get a standard Red Sea marine test kit for about $45-$50. Not much more than you probably paid for the API kit. With a good marine test kit, your readings should be different than what your getting now.
Anyway, somethings feeding the ammonia which in turn is feeding the algae. Are you feeding the tank? If so, stop. Turn off the lights for a couple of weeks and increase your CUC. The Blue Leg Hermits and the Cerith Snails are ok but they each have a particular job to do. You need different types of Hermits and snails. Ten of each. Nassarius Snails burrow through the sand and help keep it stirred and clean. They pop out of the sand when it's feeding time which is pretty cool to watch. Nerite and Turbo Snails do a much better job on the Hair Algae in my opinion as well as keeping the glass clean. Different types of snails have different shaped mouths, thus they require different types of nutrients.
As far as Hermits? Scarlet , White claw and Left Handed Hermits, to name a few, go to work on the Hair Algae and Detritus and also do a great job of cleaning up any uneaten food and dead animals. Their pincers are shaped different to do different jobs in your tank.
Make sure you do a proper acclimation of all snails and hermits.
The Peppermint Shrimp, if it's a true peppermint ( some stores don't know the difference.) is a good scavenger and should eat any small Aiptasia that might pop up in your tank. Mind I said should. Some haven't gotten the memo yet.
The Emerald Crab will scavenge for food but it's main diet is Bubble Algae.
No fish till you get the ammonia down to zero and can maintain zero.
