Those are some of the clearest pics I have seen of a clown. Great job! The snail, by seeing the "snorkle" seems like a nassarius snail. Shell seems different though, so could be a cerith snail or even a bumblebee snail. No matter what, its a good thing to have. At night look at your tank with a red light, or a flashlight with a red filter, and you should see quite a bit of new little critters running around. It is a whole different world at night in a saltwater tank. Definately an exciting experience in the beginning.
Just keep up the diligence of testing your water, do regular water changes with good water, and you should be good. Unfortunately, green chromis are known to kick the bucket quite a bit. There are many reefers in my club who like to have 12-15 in their larger tanks as a nice schooling fish, but usually loose 3-4 a month all the time. Just something that happens with them.. In groups they always seem to find the weakest link and stealth kill them when you least expect it.
You may be going a little fast on your setup though. Too many fish too quick IMO. Did you use anything like Superbac to start cycling your tank? Having that many fish in your tank while your trying to get the initial cycle started is very very hard on the fish. The clowns may make it, but may get sick in the process, but the green chromis probably won't handle the cycle from my experience.
PH, don't worry about it too much. If you use good water and do regular water changes the PH will be fine. PH also fluctuates depending on time of day/light schedule. On my tank in the morning just before lights on my PH can be as low at 7.8, but at the end of the day before lights off it will be at 8.3. Just a natural fluctuation from everything in the tank reacting to the light. PH fluctuations really matter more with SPS corals, LPS, softies, and fish can handle it much better.
With your hydrometer/refractor test, yes, that is my exact experience as well. Just get the hydrometer tested with the refractor and use a sharpie on the hydrometer to mark exactly where 1.025 is.
Fireworm, I would buy a bristleworm trap and catch them.. definately not a good thing to have. Bristleworms are fine, and good to have IMO, in low numbers. They are great cleaners, but look more pink, fireworms on the otherhand will eat many corals.
As for your nitrates, I would say don't let them get above 40, if and when it reaches that point, do a good size waterchange, 25-50%.
Do NOT get a mandarin. It won't make it in your tank no matter how many pods you throw in there. Those are very expert fish, even the most experienced reefers I know have all had problems getting them to live more than a year, even in a 7 year old, well established 150G reef tank. Those fish shouldn't even be sold in this hobby IMO. The price is low that most people want them, and they are some of the nicest looking fish color wise so I understand the temptation, but you would litterally have to throw in 2 bottles of tiggerpods a DAY to sustain a mandarin. That is $50-$60 in food a day in a FO tank without a refugium. Mandarins will eat a copepod once every 5 seconds if given the chance.
