Red planet STN

[jamgar]

For the guys that have been into SPS for a while...Do you ever get bleaching/STN at points where your coral is shaded. I have a small frag of red planet that is in the shape of an X. The bottom of the X that is shaded is white and I think it is probably STN. I have been watching it for a couple of days and it doesn't seem to be advancing...at least not quickly. The rest of the coral seems to be slowly coloring up. My alk seems pretty stable between 8.8 and 9.3. mg 1200-1275, Ca 460. I have been slowly increasing topoff with kalk in a stirrer to keep up with evaporation but since summer hit I am up to 5 gallons a day and still not keeping up. I am adding a couple of gallons of ro/di every couple of days. pH has stayed around 8 (kalk dosed 24/7). Water changes 5% every week contiuous.
I have opted to just observe for now and am thinking it was either an alk swing at some point (although all other sps look OK...still coloring up) or from natural shading.
Any thoughts

[jdg]

I have the opposite issue, some STN on a frag that faces the light source with the parts under shadow being okay for now. How is your polyp extension? I have none.

[lolgranny]

I get it on the underneath of my RP and its still kicking away.

[curlykid]

this happened to mine! in the part that is shaded there's no tissue whatsoever. when i feed my SPS i dose Restor and CoralAmino so idk what's up.