Calcium deficiency? Phosphorus? Only one plant of 3 in dwc.

[Raggedy Man]

There are 3 plants in this dwc tote. 2 bubblelicious and one blue cheese, 9 weeks and well into flower. Brown spots affecting only one bubblelicious. Water temps average 68° (I have a chiller I alternate between 2 totes). Room temp not above 80° or below 70° depending on lights on/off. Mixing GH nutes throughout this grow 1 part micro 2 parts bloom, and 1 part calmag. Ppm is at its max or they start developing leaf curl. pH has always been 5.8-6.1. rh 45 - 55%
I just did a rez change last week
Any ideas what this is and why only one plant?

 

[namvet25]

Looks like there starting to wind down and should be ready to chop soon.

 

[Raggedy Man]

Looks like there starting to wind down and should be ready to chop soon.

This particular plant IS further along than the others so if it is an ailment I hope she can make it before it gets too much worse. I can never tell by looking several times a day if more leaves are spotting or it has stopped.