Removing Heavy Metals from Aquarium Water
Get heavy metals out or render them harmless: RO/DI filtration, chelating water conditioners, carbon and adsorbing media, water changes, and the problem of copper bound to rock.
Once you know metals are a risk, the next question is how to get them out of the water, or at least render them harmless. There are four practical tools: purify the source water, bind the metal chemically, adsorb it with media, and dilute it with water changes. They are often combined.
RO/DI filtration
Reverse osmosis (RO), usually paired with a deionising (DI) stage, is the gold standard for sensitive tanks. RO forces water through a semipermeable membrane that removes dissolved ions and contaminants; household membranes achieve rejection rates around 95 to 98%, stripping out dissolved metals along with nitrate, phosphate and most other dissolved solids. The result is near-pure water that you then remineralise to the hardness your livestock needs. RO does waste some water as concentrate.
Chelating water conditioners
Many dechlorinators do more than remove chlorine and chloramine: they also contain ingredients that detoxify or bind heavy metals such as copper, zinc and lead, holding them in a form that is far less bioavailable. A conditioner that explicitly treats heavy metals is a sensible insurance step every water change, especially with copper-bearing tap water and sensitive livestock.
Adsorbing media
- Activated carbon adsorbs dissolved organics, medications, toxins and discoloration; it becomes saturated and must be replaced, not reused indefinitely
- Metal-adsorbing resin pads and chemical-filtration media are designed to pull dissolved metals out of the water
- These are run in the filter and renewed once exhausted
Water changes and the copper problem
Large water changes with clean, metal-free water are the simplest way to dilute dissolved metals out of a tank. But dissolved copper does not stay only in the water: it binds to porous rock, substrate and other surfaces and then leaches back out slowly for a long time. This is why a tank that has been dosed with copper is hard to make safe for invertebrates again; in severe cases the porous material may have to be replaced before shrimp or other inverts can be kept.