If you have a SWG then your pH will rise. Lower the TA and then add the borates. This thead on TA might help explain it
ta-what-is-it-really-t4979.html
I have never seen a pool with a SWG that did not have a pH rise over time. It is a normal effedct of running a SWG. Keeping the TA low does not eliminate this but does slow it down and adding borates slows it down even more.
How often are you adding acid now (or more importantly, how often are you testing your pH and at what point are you adding acid--be honest here!

) It is NEVER a good ides to let the pH in a SWG pool rise above 7.8 for many reasons but the first is it will help prevent scaling in the cell and in your pool!
IF you post a full set of test results it can tell us more.
Why are you adding borates if not for the pH control? Algae control in a salt pool is a moot point because a properly set up, balanced, and operating SWG pool will just not go green, so this would not be the primary reason to add borates!
You say that you want to keep your FC and pH in check. Borates will not affect the FC. Your CYA and run time will. Make sure your CYA is 80 ppm for the best results here!
pH control in a SWG is primarily a function of the TA. Lower the TA and you slow down how fast the pH rises. The bicarbonate buffer we call TA will cause the pH to rise to about 8.2-8.3 over time since this is where it wants to rest. Nature of the beast! The lower the TA the slower this occurs but it will eventually occur in any pool that has bicarbonates in the water unless something else stops it (such as the addition of acid, which could come from many sources, including bathers!)
The addition of borates adds a secondary buffer system that causes the pH to drop but it is not as strong so the net effect is that the pH will happily hang out at about 7.7 for an extended period of time. The bicarbonate buffer eventually wins out and the pH rises. That is why I say to lower the pH when it hits 7.8.
Hope this explains it.