I think, Dirk's advice makes perfect sense.
Don't forget that you are are at the very end where a SLAM is still just possible. Your target CYA is 80, interpreting your last CYA test conservatively, you're assuming 90 for the SLAM. Since you really just had a hint of algae, we thought that it makes sense to proceed with the SLAM.
But I think you're getting the picture now, why we would ask someone joining TFP with a swamp and CYA 90 to replace some of the water to get CYA down before starting to SLAM. It is difficult to maintain the required high SLAM levels.
This is also one of the reasons why TFP recommends the higher target CYA of 80 only for SWG pools. With the more constant chlorination throughout the day, the risk is much lower to slip below min. That justifies to take advantage of the much reduced UV-losses at higher CYA, allowing to run the SWG on much lower output, which in turn will extend the cell's lifetime.
For a pool that gets a manual dosage of chlorine every 1 to 3 days or so, the risk is much, much higher to slip below min, resulting in a massive algae bloom because it might take a few days to realise what's going on. The potential chlorine savings at higher CYA apply of course also to non-SWG pools, but the risk of having to SLAM is much higher - and also the extent of an algae infestation is likely to be much higher than in your case - which at high CYA is not much fun. That's why TFP doesn't recommend higher CYA for liquid chlorine pools.
And for SWG-pools where TFP thinks that it's worth taking advantage of the reduced chlorine demand at higher CYA, it's very important to ensure to never let FC slip too low. Depending on the individual setup (UV-load, bather-load, water temperature, testing frequency, etc), this might require a higher personal target-FC than listed for SWG-pools in the FC/CYA-chart. That's perfectly fine - it might cost a bit more in daily chlorine production, but if that's what is required to avoid slipping too low, then it's worth it.
It could make sense to confirm your CYA again. You were maintaining very high chlorine levels for some time now, which results in accelerated oxidation of CYA. Since you were only conservatively assuming CYA 90, you might actually test your CYA safely as 80 now, which would make your SLAM a bit easier.
When testing CYA at very high chlorine levels, you should neutralise the chlorine in your sample first, because all that chlorine attached to CYA can prevent some CYA from clouding out. You can do that by adding a drop of the buffer solution from the TA-test to the 5ml water sample before adding the CYA reagent.
Keep up the good work, you're doing great
