you can add shells toy our tank, sure.
But, hermits are really finnicky when it comes to their homes.
I have a TONNE of shells in my 72 gallon reef, like 10 per hermit of all shapes and sizes and my hermits still prefer to take the astraea and margarita shells.
I guess maybe it's something about a fresh shell versus one that is "used".

I used to think it was funny, but with snails costing between 2 and 3 bucks a piece and hermits not even being a neccessary addition to a clean up crew they have lost their humorous appeal.

That definitely will add up after some time. With the cost of livestock, any dollar that can be saved by not having to replenish snails is a good thing.

i think the fresh water shells are to soft/brittle for their liking. i have some, one is currently being used but he shaped it to fit by breaking all the weak parts off.

Good idea on the rubble instead of the media in the canister. Nitrate factory (with media)!!!

When you decide on inverts, you need to decide whether you'd like hermits or snails. They don't co-exist very well as the hermits kill the snails, as they prefer escargot to algae and detritus. You can't blame them really!!

I prefer snails as hermits have other drawbacks as well. I keep Astrea, Nassarius, Cerith, Margarita, and Ring Cowries. I have mixed feelings on the Margaritas as they are a temperate species, and don't survive well in the tropical temperatures of our reefs. The higher temperatures speed up their metabolisms, and they live a much shorter life than they should. So, I feel bad putting them in my tank, but they are AWESOME algae eaters! The only reason I have them in my tank is because they were sold to me as a different species. When they die, I don't think I will replace them as I feel too cruel!

ok. Thanks for the info on the magaita snails. Didn't know that. Is there a "rule of thumb" for how many snails to put in a tank? 1 per gallon? 1 per 5gals? Do they need to get included when I am figuring out the bioload?

They do add to your bioload, but not nearly as much as a fish does. There isn't really a rule. The 1 per gallon thing is a joke...they'll starve to death. Start with a couple of each type you want to try and go from there. My Astreas have been very hardy. I bought three when I first set up my 33g in Dec 06, and they're all still going strong. They are an uncommon species called Astrea caelata. To give you an idea, I have 14 snails in my 33g. I also have an Orange Lip Conch. I find my Astreas, Margaritas, and Conch do the most work. The Nassarius population rotates due to them dying off (maybe 50% per year), Cerith as well although at a lower rate (maybe 25% per year). I don't find the Nassarius do a whole lot, other than picking at uneaten fish food, but my Peppermint shrimp does just as a good a job. The Nassarius also churn the sand a bit, but I find my Conch does 10x better job of that! I won't replace my Nassarius or Cerith in the future. So here's a breakdown for you:

Orange Lip Conch - churns the sand, keeps the sand clean, cleans the lower 1 1/2" of the glass (as far as he can reach haha)

Margaritas & Astreas - I think do pretty much the same thing, which the Margaritas being a bit more efficient. They do a good job of the green & brown algaes on the glass and rocks.

Cerith - stick to the glass, and don't do a whole lot.

Nassarius - stick to the sand, and due their small size, don't do a whole lot. They do churn the sand a bit, and eat some fish food, but other critters do a better job imo.

Stomatellas - awesome algae eaters, and will reproduce in the tank. My favourites. :)

Peppermint shrimp - Pretty much attack uneaten fish food. Good scavengers. Often eat small aiptasia, but also ate my Stomatella snails. :(

Cleaner shrimp - Good scavengers, will also clean some fish of parasites.

i do have to disagree with the choosing of snails of crabs. i have a 34 G and i have over 20 snails of 4 different types and 15 hermits of 3 different types. i have seen them hassel the snails a little but they are usually able to get away unless they fall and are overturned. i have only lost 2 margarita snails in the 9 monthes ive been set up. all were added at about the same time.

Just my opinion. i do however feed an exces of pellet food once in a while as the hermits and shrimp seem to really like it.

PS i think i have lost more hermits to hermits then snails to hermits. as the 2 billion shells in my tank arnt good enough so they fued all the time.

Interesting. I also never knew that about margaritas. To bad,as I find them to be a good cleaning snail, unlike so many others we buy.

Yes, it is too bad...I think they are the best algae eating snail I have! They are very active, and you don't see them in the same place for long. I keep my tank a bit cooler than the "average" reefer does, at 77 degrees, but "temperate" is much cooler than that!

Yes, mine is seldom over 78.5 also. I was just going to purchase some more but may look for another now.