125 stocking plan?

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I have a 125 gallon tank that the water chemistry is really starting to look right (it was set up for 6 years but the water changes were twice a year at best) when i got it the nitrates were showing at an extremely high 160ppm. I now have them down somewhere between 0-5 ppm and everything seems to be doing well, had a minor diatom bloom that lasted a couple days but it declined. At the moment i have a 5 head frogspawn coral about 4 inches tall, a couple anemones and some assorted zoas and all is doing very well. For fish there is a 4 inch seargent major (going away, too aggro) a little 4 stripe damsel and a percula clown. I want to stock it with a few more corals but i want the main purpose to be fish. Heres what i want feel free to tell me if im dumb. I want to keep the clown. Add 3 pajama cardinals, either a yellow or blue tang, a longnose hawk and a dwarf fuzzy lion. I know the lion is kinda a crapshoot but i used to have one and i really liked it. I figure at worst he will eat the damsel and maybe the clown.

 

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and for the love of god can someone tell me what is making these little sand snorkels that i find sticking up every morning. Ive watched a little puff of sand come up out of the snorkels then tried to dig up what was making it with no success. I have even watched the seargent major dive at it and come up dry 4 or 5 times. Whatever it is its fast moving under the sand.