I think the way it usually works is that pH goes up when nutes are consumed and goes down when water is consumed. I don't know if using 5.3 water is such a good idea. Shoot for about 6.3 when water and nutes are mixed, then add that to top off. ppm drops because adding water dilutes the mix, so your solid particles (ppm) goes down. I suspect that your curling leaf problem might be due to low pH. Mix water and nutes and see what pH is, then adjust if necessary. I bet you could let pH get to 6.8-6.9 without problems, however most info I've read says to shoot for a fairly steady pH of around 6.3, but don't sweat it too bad if it goes up. That might just mean to add some more fert. If the water level drops visibly, then top off some but you should use a mix of water and nutes, not just water as doing this will probably give the best pH/ppm maintenance.
Do you see how this works? If the nutes are too few, ppm is low and pH is high.
If pH is low, nutes are too many and water too less. At least this is how it usually works. pH and ppm tend to work opposite to each other. You need high ppm to make pH low using just nutes alone. More fert makes the water more acidic (low pH). It's not the amount necessarily but the low pH is telling you that there is more fert molecules per unit of water and making the water more acidic. High pH means there is greater dilution as water tends to be right around the middle with a number of 7. Number 1 is very acidic and 14 is very alkaline and 7 is in the middle, which is usually what water is. When you add ferts to water the pH starts to drop as the water becomes more acidic. Ideally you grow with a stable pH of around 6.3 and enough ppm to feed a hungry plant. I think low pH has been known to cause leaf curling.