Time for a little study.
Do some more reading and you will begin to understand tha CH in pool water only goes one way, and that's up. There are only a couple way to reduce calcium in pool water. One way for calcium to leave is for the water to be drained and replaced with lower CH water (either tap water, softened water, or RO treatment). Another would be for the calcium to precipitate as scale on the surface of the pool (which you don't want). That's it. So you can slow the rise of CH by using low CH water as make up for evaporation and splash out, but unless you have an huge amount of splash out its still going to rise.
The secret to preventing scale (or in your case additional scale) is controlling CSI. CSI stands for Calcite Saturation Index. If you enter all your test results and readings in Pool Math, you will see the calculated CSI near the bottom of the chart. While the CH tells you how much calcium is in the water, the CSI tells you if that calcium will (if correct) stay dissolved in the water or will (if too high) precipitate out as scale on the pool surface. Also (if too low) the water can actually damage the pool by dissolving calcium right out of the plaster. The CSI is a calculated using CH, TA, pH, CYA, Temp and other factors. The one factor of these over which you have the most control is the pH. Learn about CSI and how to control it and you can master the art of preventing scale. As CH rises in water, maintaining a balanced CSI becomes more and more difficult, but I and others here have been successful in maintaining scale free pools with CH well in excess of 1,000.
Since the factor most critical in balancing CSI is pH, you must maintain stable control of pH. Scale in a pool is usually a sign that the pH was allowed to get way too high and left there for way too long. In a pool with a SWG the pH will have a tendency to rise. Slowing that rise and buffering rapid pH changes can be accomplished by maintaining a relatively low TA.
TA normally goes up and down with changes in TA, but there is a way to lower it. You lower the pH to about 7.2 with MA. Then use aeration to raise pH back to about 7.8. It seems that when aeration raises pH, it doesn't take the TA back up with it. So by repeating the process the TA can be lowered.
Now that is the beginning of learning how to prevent adding more scale to the pool. You should also note that when the CSI is at any level below the ideal zero number, you may actually see an increase in the CH due to softer scale being redeposited into the water.
End of today's lesson.....
...maybe that 1.5 gal (much over pool calculator suggestion) did the kill? 
