Its the water temp.. and the angle of the sun. This is the time of the year when things are warming up and the sun is creeping higher in the sky, so the affect of UV degradation becomes more pronounced. Its easy to think you have your SWG dialed in.. and then things go south because you forgot to take into account the effect of the change of the seasons. My second year with my SWG was like that as I tried to figure out how to adjust for the changing conditions.. but its easy.. just turn the % knob up a little as your FC starts to drop due to the demand.
This is a great post. Tegguy, be prepared to tweak your SWG % output quite a bit until you've got it dialed in. Even at that, any change in the pool will cause you to change % output.
In my case, I live in Las Vegas but my pool has an electric cover on it so the water's usually not exposed to sunlight. I'm also out of town quite a bit so I can run my SWG at 20% for 2 hours a day and it's fine; keeping my FC stable at ~7-8. Until the pool gets used (I usually use it at night so it still doesn't lose much chlorine due to sunlight).
This last week, we've had out of town guests. I wasn't home the first couple of days (they used the pool during the day) so I didn't have a chance to check chlorine levels. When I got home, FC was down 1. I set my SWG at 100% and started running my pump for 24 hrs/day. The pool continued to be used daily during the day so it took me ~3 days to get the FC back up to ~7-8.
I've now got my SWG set to run at 100% with my pump running 12 hrs/day. Since our guests will be leaving in a couple of days, I'll wait until they're gone to dial back on my SWG output.
Now, as far as your leak goes. Please make sure to rule out bubbles from the SWG. SWGs produce bubbles as a byproduct of the chemical reaction that turns salt into chlorine. There are technical papers out there that explain it much better than me, but I really noticed the SWG bubbles in my pool the last couple of days.
For my pool, the SWG bubbles are very small. They have been coming out of one of my floor jets constantly while I've been running the SWG ... I hadn't noticed this before, as I rarely have to run my SWG this much.
I've had a leak before and the bubbles were much bigger for me and they came out of multiple floor jets.
So just to make sure that those bubbles are a leak and not your SWG, turn off the SWG for quite a while (I don't know how long it takes for the SWG bubbles to stop so maybe give it 30 minutes with SWG off?) while the pump is running and see if you still have bubbles. That would definitely allow you to rule out bubbles from the SWG.