Most of the main Coir brands have ND to very low levels of heavy metals-Hydrofarm and Botanicare are two that I use for that reason. Surprisingly, canna is a bit higher but still not bad at all. BUT, some brands have failed testing miserably, but most of those were premixed bags of coir/perlite. Perlite is one thing people overlook a lot, but can be quite polluted with metals. Maxibloom was formulated for tap water use, and the acidity is one of the big selling points-I still have to add citric acid to get the PH where I need it. It's not great for use with RO water for that reason, although if you have extremely alkaline Tap or well water, you can always mix some of that into your RO to give it the bicarbonates/carbonates it needs to buffer the Maxibloom and keep the PH steady.