I'm at a loss for what to do here.

I've got an in ground fiberglass pool.

A few days ago my water went milky colored for no apparent reason. I had been adding some CYA though. overnight test showed a loss of 1.5 ppm. Began shocking. Water is still murky at this time.

Went out this morning to check on things and noticed my pool surfaces both horizontal and vertical have some type of white powdery residue on them. The powder wipes away and you can see the area that was wiped. When looking at my hand there is a bit of white on it. The substance is almost like baby powder in the water.

I did backwash last night and had to add some new fill water.

What could this be? What to do? Help!

Morning tests

CH 175
FC 17
TA 110
PH 7.3
CYA last measured was 45. ran out of drops. waiting for taylor shipment.

Likely dead algae; brush it up and let your filter take care of it.

I backwashed last night and the water ran white for a minute or so then cleared. I filled the pool back up and added more chlorine to shock level. I brushed the walls and steps this morning. Pool is not clearing yet after a few days of shocking. I will stick with it. My TA was up this morning since my fill water TA is above 200. I'll have to work to get that down later.

I read a thread on her from someone who had a similar issue with both his and his sisters fiberglass pools. His resolution was to raise the CH to 300-350 and add some scale/stain treatment along with regular brushing. This suggestion came from his pool guy and the manufacturer. His chalky issue cleared up after a few weeks. He did indicate his pool got cloudy after swimmers stirred things up, but don't know if his water was cloudy regularly like mine.

I'm at a bit of a loss as to whether my issue is similar (sounds like it) or if it is just an algae issue. I had been towards the end of an ascorbic acid treatment when this began. My water was clear through the process and I believe I had slowly raised the FC back up to neutralize the remaining acid after the stain was gone. I did this until I was able to hold FC overnight. Since then I have been maintaining the chlorine, keeping my TA around 90, and my PH 7.2. I did add some stabilizer just before this whole murky water/chalky surface began Sunday. I can't see how the stabilizer would cause this. While swimming Sunday I did find some small hard particles of what I believe is the stabilizer crystals on the bottom of the pool.

Still no progress despite shocking. It has been difficult keeping the FC up during the work day when not home. Don't know if this short lack of shock level chlorine will prolong the process or not. Going to do the overnight test tonight. Shock level for CYA of 40 is 16.

What was the last FC & CC test result?

Since you are not able to babysit the pool for shocking, you should shock at least twice a day. I suggest you shock early morning and then in the evening when the sun is off your pool. Then before bed, you could raise it back up to shock level. btw, if you have a cover, make sure to leave it off during the day.

OCLT tonight sounds good. Between that and the FC/CC tests, you can rule out/in organics.

If you rule out organics, maybe you need to pursue the CaptJohn process (from the other thread mentioned).