Ahhh tap water! Prolly FULL of phosphates depending on your location and water quality could be very high. (Agriculture areas can have lots of phosphates from farm runoffs.) Def agree 86 the Tap water, do water changes ASAP 50% to start and maybe in another two weeks another 50%.
Mmm... also...Instant Ocean? Is it Instant ocean REEF Chrystals now?? I see a bucket there... Well if so then....there's your problem! lo.... JK. maybe not, but you should be aware they have had quality control issues in the past, I would be WARY of using that product. Go with SeaChem or Oceanic salt mixes. Some have had no problems with I Ocean others stay clear of it..I have heard people having problems with that Oceanic salt mix a few years in the past... Bad Batches with too high phophates and or HIGH ALK killing the tank and or causing EXACT problems like this. Not saying this is your cause, but could be.. Do a phosphate check, it bet they are high
http://www.reefland.com/forum/reef-aqua ... blems.html
I have had good success with both Oceanic and SeaChem, you might consider switching salts too, and by ALL MEANS as other say only USE RO/DI WATER.
SM is also right about even the SAND and LR having and leaching phosphates, and also he is right about your tank being young...still cycling....
Do a water change with a different salt product using RO water.. If you cannnot make it BUY it at local water store. Just make sure its RO.. if you can get RO/DI ((de ionized- de ionization helps remove excess minerals) RO/DI is even better to remove the minerals (most water stores dont always use DI filters) Some will hook you up with temp bottles too if you give them right back.. I have a local store that will DELIVER me 10 5GA bottles I dump in clean new 40 Gallon trash can with new salt, then i aerate, then use small pump to pump back into tank.
Salt Prices are pretty much the same too. Might have to buy online if your local store doesnt carry SeaChem or Oceanic.. Try marinedepot.com
Also, your tank is also pretty young and you can have spikes of growth like this early on no matter what you do so give it some time, youll be fine