I've been using an HR Copper Checker for my QT tank and as of late I've been having to check maybe up to 4 times just to get a semi-accurate reading and I'm wondering what's the best way to clean my cuvettes? I know there's Hanna's cuvette cleaner solution but is this really worth it or is there a much cheaper and effective way of cleaning them? I just dip them in distilled water and wipe with a fine, microfiber cloth and it's not really making much of a difference. Any help would be greatly appreciated!