ICH Problem In 24G Nano Cube
I have a 24G nano cube, 30 lbs live rock, 25 lbs live sand, 1 Lysmata shrimp, 1 peppermint shrimp, 1 serpent star, snails, hermit crabs, 1 clownfish, 1 coral beauty, 1 blue tang, and 1 mandarin green goby, no corals as of yet.
<... the Centropyge Angel, Tang... even (especially!) Mandarin can't live in this size volume>
All fish are relatively small 1 to 3 inches at the most. Three weeks ago, I immediately took out a domino damsel (used to cycle tank) after noticing white spots which I assumed to be ich.
<Too late... once noticed, already infesting your system>
Could the domino have spread the disease to other fish or to the tank since I took him out as soon as I noticed spots?
<Yes>
Could inverts such as shrimp, serpent stars, snails, and crabs carry the disease?
<Mmm, not carry per se... but can be vectors, physical carriers... as well as the water that they might be transported in...>
Could they have become infected? I thought I was on the clear, but on Sunday 2 weeks after I took the domino out, I introduced the coral beauty, and blue tang together to the main tank. All was well, and on Wednesday after coming home from work, I noticed the coral beauty, and blue tang were covered with ich. What happened? Did they catch the ich from my system as the crypt reached the theronts stage? 
<Bingo!>
or did they carry the ich already and showed signs soon after I introduced them in the tank?
<Doubtful... but yes, a remoter possibility>
Why don't the clownfish, and goby show any signs?
<Mmm, they're "stronger"... the goby is "slimier"... they will contract the ich in time, with debilitation, further cycles of the parasite>
I am so confused. I don't see signs of ich on the clownfish, therefore we can assume that the new fish carried the ich in, but then again, the clownfish doesn't come anywhere near the sandbed. What do you think?
<That our economy is in trouble, that there's too much government...>
I've read the section on crypt, but I am so confused regarding certain issues.
<Mmm, take all a "bit at a time"... your situation is not uncommon (unfortunately) and you obviously (from reading here) have a good mind... capacity to understand what has gone on, can go on... what your choices are. Of course, would be great to go back in time, dip/bath, quarantine new livestock...>
Here is my main question, does ich need to be transmitted to a fish, or can an "ICH FREE" fish develop ich on its own???
<Great question... Marine ich, "Cryptocaryoniasis" must need be transmitted to an otherwise non-infested system... put another way, there are specific "ich-free" systems, fishes... And for thoroughness sake, freshwater ich (Ichthyophthiriasis) is actually capable of "lying dormant" and surfacing given enough balance in its favor for expression>
I plan to place all the fish in a QT tank and treat them, should I move the serpent starfish also to the QT tank, or any other inverts as well? Do you have any further advise? Much appreciated.....
<To keep reading... no to moving your invertebrates... Bob Fenner> 

Re: ICH Problem In 24G Nano Cube
Hey Bob, the economy will always bounce back, but I don't know about our government, you do have a point.
<Heeee! Just ask the Soviets, or the Romans for that matter... what happens when the gov't spends more than 20-25% of the GDP... on to fish>
Thanks for all answers. Tonight, I was able to catch the blue tang, and I gave it a freshwater dip for approx. 10 min, but seems that the white spots are still there. Were the spots suppose to disappear, if so should I try again?
<Mmm, the spots are actually the fishes' reactions to the ich parasite... sometimes go, sometimes no>
I used a Meth. blue solution with treated tap water, but I have no idea how much the concentration was.
<Not important... read here: http://www.wetwebmedia.com/methblueart.htm >
I dropped 1 drop to make the water blue. I did use treated tap water with the same temp. and pH as my main tank water as the freshwater dip. I'm trying to set up a QT tank, but until then I thought I'd give the tang a dip to rid it of the ich that it has so badly.
<Mmm>
I don't think he's going to make it, and I know you said he's probably not right for this size tank. But I'm stubborn to make this work....good news is that all fish are eating well. We'll see about tomorrow.
<Bob Fenner>