for snails, i prefer cerith, margarita, and nassarius. cerith and margaritas typically clean the rocks and glass while nassarius bury themselves under the sand. another on i like are conch because they clean the sand bed for a living. they also stir up the top layer of sand while they are at work. i would stay away from astrea snails because they do not tend to do well with tanks that have sand. in the wild, they live in pretty rocky areas, and are rarely, if ever, exposed to sand. when they fall, they are unable to right themselves up so if and when they fall on the sand in your aquarium, they will be stuck upside down and eventually die. you should also take note that since your aquarium is still quite new, you shouldn't add any snails until your tank is a little more established, as you won't have much algae for it to snack on. and even though you will start to get diatoms later on in your cycle, they will eat it up pretty fast and run out of food pretty quickly.
for hermit crabs, there are mixed feelings on them. blue legged hermit crabs one of the only hermit crabs that are reef safe, but if they do not have enough food, they are not above killing other inverts for food, even corals. they will also kill any snails they want if they are looking for new shells to inhabit. i personally do not like hermit crabs, as they tend to knock down corals that i haven't glued on to the rocks. when i first started in the marine side, i loved these blue legged hermits as they looked really cool while they were scavenging for food. eventually the food levels for them went down and they started killing my cerith and margaritas and also took their shells! so if you do decide on adding hermits to your tank, make sure you have a lot of empty shells that range in different sizes (well, obviously not any smaller than the shells the hermit is currently in).
a common mistake people make when they start adding their CUC is to add sea stars, or star fish (whatever you want to call them
). this is because the typical sea star cannot survive without proper feeding. stars are scavengers, but aquariums, especially those of your size, do not have enough left over food for them to scavenge. another problem with sea stars is that some can grow way too large for aquariums. if you really wanted a sea star, wait for your tank to be at LEAST 3 months established, do some research on the ones you are interested in, make sure they do not get bigger than half your palm size (big specimen are not above eating sleeping fish!), and to make sure they are properly fed every day (most are nocturnal so you can feed it when it's lights out so the fish do not compete for the food).
crabs are generally not reef safe, and if they are, you should definitely keep your eye on them anyway. mithrax (emerald green crabs) are one of the few crabs that are considered reef safe and are even known to munch on the invasive bubble algae. but unless you have a bubble algae issue, i would steer clear of crabs altogether.
last but not least, nudibranches (plural? lol). people are often tempted by nudibranch as some have stunning colouration. the problem with nudibranch are that they have very specific diets in the wild. many people are still unclear what they eat specifically. the ones we do know about don't live for very long in aquariums, as aquarists are not able to supplement their dietary needs. the same goes for sea cucumbers. it is much too difficult to keep these creatures so it is not recommended to purchase them at all. some aquarists purchase specific nudibranch, such as the berghia nudibranch who are known to eat aiptasia anemone, and pass them down to other fellow aquarists who have aiptasia problems, so that they are not starved to death staying in one aquarium that cannot feed them properly.
in conclusion (
i know i've gone on for long enough), a common number of snail/hermit ratio are 1 per gallon, but i personally would never go over 1 for every 2 or 3 gallons, as they would most like starve themselves, especially the hermits. so i think a good number for you to start with would be less than 10 snails and maybe 5 hermits. again, with the snails, add them after your tank has cycled properly.
thanks for reading and good luck!!
