Did you cycle your tank?
Make sure you dont add to many fish/corals/inverts quickly...your tank must build up its system, and mature before you load it with fish/corals.
I would do a 10% every week, or 5% twice a week, for about 2 months, just to make sure you dont have a parameter issue.
Do you have to different types of clowns in a nano? Looks like a occ. and a perc.
What type of lighting do you have?
What type of tank/how big is it?
Do you have a sump/fuge?
its look like its the 14 gallon biocube ... lighting looks stock which means it is 2 power compants 48(2 x 24) watts... on the top he wrote 8 weeks in i think thats fair enough... just dont know if the fish n corals were placed in the beginning... the sun coral you have requires spot feeding. It is a difficult coral to start off with. I have the same tank I only have one clown and one watchman I felt anything more would be overstocked esp since the clowns can be a bit aggressive/territorial. As you go on I would slowly take out the bioballs in the back and replace it with some media (i.e purigen and rowaphos) in order to help maintain healthy parameters. Stick with zoas and leathers and some LPS (i.e Acans, you already have a plate coral you can go with frogspawn, candy cane) Other then that good luck!
Nice! Is that a sea urchin to the right?Anyway i'm not trying to stir up sand here but when i first ventured in the realm of marine inhabitants my first book was The Natural Reef Aquariums by John H. Tullock.It's about 10 years and there is some step by step ways of setting up small and large reefs you may find it helpfull. Good luck.
no more fish, waterchange often and get rid of the urchin all he is going to do is knock stuff over and sting you. you should not have gotten the sps (looks like birdsnest in pic) not enough light or flow in that tank. Give them a better home before they die. and dont forget to feed the sun coral, that needs high flow too.