Tin showed up on your ICP test. Here's where it's coming from.

You open your ICP report, scroll past forty numbers you feel fine about, and hit a red bar next to an element you've never once thought about: tin. Then you search "tin reef tank" and the first results are toxicology papers about poisoned oysters and forum threads about lost coral colonies. Deep breath. Most elevated tin readings end with someone finding a rusty screw or swapping a length of tubing, not with a crashed tank.⁶

Quick disclosure so you know where I stand: I run BioForge, and Decode, our $39 report-reading service, exists precisely for moments like this one. I'd obviously rather you use it than panic-buy equipment. But everything below is the same process I'd walk a friend through for free, sources included, so you can run the whole hunt yourself.

The three things worth understanding

1. Tin in your water came from inside the system. Natural seawater carries almost none, and clean salt mixes contribute almost none. An elevated reading nearly always traces to something you installed.
2. The toxicity literature is mostly about a different tin. Organotin compounds like tributyltin are ferociously toxic to marine life and are the reason tin has its reputation. Inorganic tin, the more likely form leaching from your plumbing, is far less studied. Your ICP can't distinguish them.
3. The fix is a hunt, not a product. Confirm with a retest, find the source, remove it, dilute with water changes, then let the next test tell you whether you got it.

Why tin has its reputation, and what your report actually measured

The reason "tin" and "reef" make such a frightening search pairing is tributyltin, or TBT. For decades it was the active ingredient in antifouling boat paint, and it turned out to be one of the most destructive compounds ever released into coastal water. Peer-reviewed work has shown TBT inhibits coral fertilization and blocks larval metamorphosis at concentrations around 2 micrograms per liter,¹ disrupts reproduction in marine snails at nanogram-per-liter levels,² and damages immune function across marine invertebrates broadly.³ The World Health Organization flagged organotins as a serious marine hazard back in 1990, and TBT has since been banned internationally.⁴

Here's the part the horror stories skip: your ICP report measured total tin, the element. It cannot tell you whether that tin is an organotin like TBT or plain inorganic tin leached from a stabilizer in your plumbing.⁵ Those are very different animals. Inorganic tin is poorly soluble, poorly absorbed by organisms, and has nothing like TBT's documented toxicity. And nobody has published a dose-response curve for inorganic tin in a reef aquarium, which means every "safe level" you'll see quoted on a lab's color scale is an educated guess, not a measured threshold.

So an elevated tin number is neither harmless nor a catastrophe. It's information: something inside your system is shedding a metal that doesn't belong there, and things that shed tin often shed other stuff too. That's the honest reason to act on it.

The usual suspects, in order of how often they're guilty

Years of forum detective work have produced a surprisingly consistent lineup. The community's most useful rule of thumb: look at what else moved on the report.⁵

If tin is the only metal elevated: think plastic

Tin compounds are used as heat stabilizers in some PVC and vinyl products. Hobbyists have traced isolated tin readings to flexible return tubing, PVC pipe and fittings, skimmer bodies, and kalkwasser reactor parts.⁵⁷ New plumbing is a prime suspect: leaching is usually strongest when a product is fresh. If your tin reading appeared a test or two after an equipment install or a re-plumb, start there.

If tin rises alongside iron, copper, or zinc: think corroding metal

Solder and alloy parts contain tin, and rust events rarely leak one element at a time. Confirmed sources in community threads include rusting algae magnet cleaners, degrading pump wetsides, a metal screw inside a ball valve sitting in the sump, and cabinet hinges corroding above splash zones.⁶⁷ One reefer's tin problem ended entirely when a single valve with a hidden metal screw came out of the sump.⁶ Pull your magnets apart and look for rust weeping at the seams. It's the most common single culprit I've seen.

Small tanks concentrate the problem

The same leaching part sheds the same milligrams into 30 gallons or 300. In a nano, tin builds several times faster, which is why small tanks dominate the elevated-tin threads.⁵ If you run a small system, weight your suspicion toward whatever touches the water the most per gallon: tubing, pumps, magnets.

The fix, in the right order

1. Confirm before you demolish. One elevated number on one report, with healthy corals and no other metals moving, can be sample contamination or lab noise. Retest with the same lab. Same lab matters, because trace readings don't transfer cleanly between labs, something I covered in the ICP comparison. Two elevated results in a row is a real signal.
2. Hunt with the report, not a flashlight alone. Tin alone, inspect plastics newest-first. Tin plus friends, inspect metal: magnets, pumps, valves, hinges, anything rusting within drip distance of water.
3. Remove, then dilute. Take the source out, then run a series of water changes with salt mixed in containers you trust. Dilution does most of the cleanup work once the input stops.
4. Bind what's left, optionally. Metal-binding media like CupriSorb can pull residual tin and hobbyists report it working.⁵ It's a mop, not a fix. Use it after the source is gone, not instead of finding it.
5. Retest in four to six weeks. A falling number confirms you found the source. A flat or rising one says the hunt isn't over. Either way, the retest is the verdict, not the water change.

The pattern here is the same one that runs through everything we publish: a single reading is a snapshot, and snapshots don't make decisions. Trends do. Tin just happens to be the element that teaches people that lesson with the most adrenaline involved.

Common questions, answered plainly

Sources & further reading