I would be interested to know what your alkalinity is. If it is up around 9 dkh (~ 3 meq/l) and your daytime ph is only 8 then you have somewhat elevated CO2 levels. While interesting to talk about, I don't think this has anything to do with your fish losses.

If I read your post correctly you have lost...

1 algae blenny (lawnmower blenny I assume) after having him about a month - this is about right on schedule for him to starve to death. They are tough to keep without plenty of filamentous algae for them to feed on.

4 Green Chromis - contrary to what is often said about them, I have found chromis to be a rather high loss fish. They are dirt cheap and collectors/wholesalers often pack them into bags to save on shipping and keep them cheap. So they can suffer from a variety of stress related maladies. Probably because of the way they are handled/shipped they are prone to a parasitic protozoan called uronema. Uronema is too small to be seen with the naked eye, penetrates through the tissue and attacks vital organs causing sudden death. There is no effective treatment for uronema and it can only be positively identified with a microscope.

So what am I telling you? If these are the extent of the losses you have had, I would not consider that abnormal for those species. I also do not consider a fish "established" after only having them about a month. It could have been only 5 weeks or so since they were taken out of the ocean, shipped thousands of miles to a wholesaler, tanked & then rebagged and shipped to the retailer. All the while being tossed around by the air cargo guys - there's a reason the styrofoam shipping boxes are usually busted. Then finally the fish is tanked again at the LFS, then bagged again and sent home with you. To be honest, I'm impressed any fish can live through it all.

That hairy crab is cool...but will take out small fish if he gets a chance.