It’s not a simple issue at all.
1. Lots of people have shown increased Al on ICP testing after using MarinePure, but lots of others have shown no increased Al. Some have shown increased levels for a while then back to normal. Some have argued you need to wash/soak thoroughly first and this helps, some say it doesn’t help. Ryan’s test is useful but did he thoroughly wash/soak?
2. When ICP tests show aluminum it doesn’t tell you anything about what form it is in, just overall elemental Al. Some forms are proven toxic and others are proven safe/inert. The manufacturer says only the safe kind could even possibly be there, but I’ve never seen data from them or others to prove it either way.
3. The toxicity studies that are out there show effects on softies, not SPS or LPS as far I’ve seen, and at much higher levels than the ICP tests are showing. That doesn’t at all prove lower doses are safe.
4. How are blocks being treated in your sump? They are weirdly fragile and will start to come apart if not handled very carefully. Could vibrations in the sump, periodic bumping when doing maintenance, etc release more?
All that said, Ryan’s point is good that since we don’t know if they are toxic sometimes but we do know they aren’t necessary, then don’t use them unless you have a compelling reason to. I had a large block in my sump and recently removed it. My Al was nice and low but my lithium was high for some reason. Not sure if it’s related.