Pink slime!

[waterbear]

Thanks waterbear. My TA tends to drop over time, so I can just not adjust it whenever it falls to 70, then.

That is because you have bee just dumping in acid and doopping the pH too low when you add it. When you add acid you lower both TA and pH but you lower TA MUCH SLOWER than pH. Another reason to not drop the pH as much...if you read the stickly on the procedure to lower TA is it to:
Drop the pH low (7.0 to 7.2) to lower TA AND pH
Aerate to raise pH without affecting TA by outgassing CO2
repeat until TA is where you want it.
AS I said before, the LOWER you drop the pH the MORE you outgas CO2 and the FASTER the pH rises. What I did not add to that is the FASTER the TA will drop!

If you only want to drop the pH from, say, 8.0 to 7.6 then use the acid demand test in your K-2006 and get an idea of how much acid is needed to lower the pH. I think you will find you have been overdosing on acid! Once you do that I think you will find that your TA is much more stable. It is normal for TA to drop over time but it should not need upward adjustment very often at all if you are not using an acidic chlorine source like trichlor. What is the TA of your fill water?

As far as your CYA and FC, remember this is a pool, not a science experiment. Keep it simple and don't lose sleep over it Raise the CYA to 80 ppm and run your FC between 4-5 ppm and you will be golden.
Drop the TA to 70 ppm
Keep the CH between 400-450
Keep the pH no lower than 7.6 and drop it when it hits 8.0
Keep salt between 3000 and 3500 ppm

If you do this your water will be balanced over a temperature range of about 70 to 90 degrees! Easy! (At water temps below about 75 degrees don't let the pH drop below about 7.8 if you lower pH but as long as it is below 8.0 I would not worry about it.)