Good call on the poolmath

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Its safe to have fc anywhere between minimum and slam level for your cya.
- "Min FC" is 7.5% of the CYA level
- "Target FC" is 11.5% of the CYA level
- "SLAM FC" is 40% of the CYA level
A couple issues arise with cya so high though…
If there’s an algae problem its quite impractical and expensive to treat it properly (do the slam process)
&
At maintenance/target fc levels above 10ppm it skews the ph results which means you are torn between accuracy with ph and sanitary conditions.
The sooner you perform a water exchange to get cya down to a reasonable level the better as it will result in a much simpler path.
Do the diluted cya test procedure as poolstored linked to get a better estimate on how much water you need to exchange.