brighteyes_cm said:
my husband ... ... picked up a snail... it was doing a great job on the sand and glass, and all was fine untill it hit the LR... ...Where once we had purple, red and green coralline algae now only white spots remain! Is this normal behavior for a snail? Are there any that wont gobble up all the beautiful color in our tank?
Not to worry, the snails that are sold through the aquarium trade are not capable of consuming the calcareous coralline algae. HOWEVER, if you have new live rock, look for some small urchins that may have come with the rock. They are quite capable of removing coralline algae, although this is usually not a problem, as they preferentially clean the green microalgal growths off the rock which will allow the coralline algae to develop, as well as distributing some of the algal particles from their messy eating to spread your coralline.
These Echinoderms have a specialized group of teeth in an apparatus called Aristotle's Lantern that grinds these tough algae off the rock. Some spp. are capable of boring through the rock as well. Keep your alkalinity and calcium up with a good supplemental regimen, the coralline will develop based on your lighting and current conditions in the tank. Speciation of your coralline algae will occur and this will dictate what colors actually outcompete the other spp. in the tank. If the rock spent enough time out of the water, white patches of dead coralline will develop, but I would be willing to bet that you have an urchin in your rock. Look late at night after the lights go out with a flashlight.
brighteyes_cm said:
one other question... about how long will the diatom bloom last, we were planning on picking up some more snails and such but are not sure of how many we require to keep our tank under control.
Diatom blooms are driven by the amount of silicate and the availability of nitrogenous nutrients in the water column. These blooms usually don't last more than a few days, and will disappear after this initial bloom as other competitors for these same nutrients begin to increase their populations in your system. It would be best to limit the introduction of new silicates as you have already done by using RO/DI treated water, but keep in mind that the diatoms may still return until either some sponges or other silicate needy organism(s) uptake the available organosilicates and silicon dioxides in the water column for their own structures. Once the silicate level drops below a minimal level (at total depletion to undetectable levels in the ocean), diatoms will continue to reproduce and grow, and can completely deplete the water column of silicate even in the dark. The diatoms that form tests in this silicon-depleted environment will photosynthesize when illuminated again, but will quickly die within hours. The silicate formed by diatoms is completely insoluble while they are still alive, but once they do die, the tests become 100% soluble up to the solubility limit of silicon in seawater, the excess of which is sinked in the substrate. This may trigger another cycle in a closed system, but usually the cycle is broken once sponges and snails begin to uptake these excess silicates in the water column. To prevent this cycle in a closed system I would recommend that you siphon out the dusting of diatoms from your rock and substrate surfaces as they appear, as this will export the silicates out of your system.
Go ahead and add a few snails now, but add them just a few at a time (maybe 5 to 10 at a time if you have 75 gal us or up) until you find that they are feeding well and consuming the algal growths forming in the tank.
hth.
is this normal behavior for a snail? are there any that wont gobble up all the beautiful color in our tank? 
