Water and individual numbers look good but low CSI

[Fuldo]

I'm helping a neighbor in NH with her pool. This is a vinyl pool being cared for with liquid chlorine and has a single speed pump with sand filter. It was just opened a week ago. Water was found clear after cover was removed. I vacuumed, added two gallons of 10% then checked numbers for her:
FC: 10.5
CC: 0
PH 7.4
TA: 70
CH: 100
CYA: 50
Temp: 55

The individual numbers look reasonable to me. The CSI however is -0.90. I suspect the TA and PH will increase as the water warms and the season progresses and that should improve the CSI but it will probably still end-up on the low side unless some chemicals are added. How low can the CSI be with a vinyl pool without posing problems? Should any adjustments be made now?

 

[Texas Splash]

How low can the CSI be with a vinyl pool without posing problems?

No problem. The CSI concept mainly applies to plaster pools or pools with plaster products exposed to the water (ie. shell, waterline tiles, etc). So really simply keeping the regular parameters in check is all that matters. If your friend has a heater, then a low pH (corrosion) might be a concern is there is any copper inserts, but other than that, I think those numbers look quite good for opening.

Trivia, even though it doesn't apply to her pool (vinyl), the CSI will increase as the water temp increases.