How do I get stains off the bottom of my pool?

First identify the stain: organic stains (leaves, acorns) lift with chlorine held against them; metal stains (iron, copper) do the opposite — they lighten with ascorbic acid, not chlorine. A simple test with a chlorine tablet versus a vitamin C tablet on the stain edge tells you which family you're fighting.

Why does algae keep coming back in my pool?

Because something upstream is still broken — chlorine that can't hold (often stabilizer buildup), a filter passing spores back, or algae surviving under biofilm in unbrushed corners and behind light niches. Kill-and-forget doesn't work; the pools that stay clear fix the chemistry and the brushing habit.

Will stains come out of old plaster?

Sometimes — but stains that have penetrated old, porous plaster are often permanent tenants. If the surface is rough and past its lifespan, stain-chasing becomes throwing money at a finish that needs replacing. That's replaster territory, and the honest quote reflects it.

Pool Stains, Algae, and Debris: What Comes Off, What Doesn't, and How

Not everything ugly in a pool is the same problem. Here's how I tell algae from metal stains from organic staining — and the right removal play for each, before you waste a weekend scrubbing the wrong thing.

A good chunk of my service education conversations start the same way: someone has spent a weekend scrubbing a stain that was never going to scrub off, or shocking a pool that didn't have algae. The frustrating truth is that the ugly stuff in pools comes in different species, and each one has its own removal play. Treat the wrong species and you're just exercising. Here's the field guide.

First, sort what you're looking at

Does it brush off into a cloud? It's alive (algae) or loose (pollen, dirt). Removal is about killing and filtering.

Is it a fixed mark that doesn't move when brushed? It's a stain — the question becomes organic or metal, and there's a simple test: hold a chlorine tablet against the edge of the mark for a few minutes. If the spot lightens, it's organic (leaves, acorns, berries, worms — Houston backyards supply all of the above). If chlorine does nothing, try a vitamin C (ascorbic acid) tablet the same way — if that lightens it, you've got a metal stain, usually iron or copper.

That two-tablet test saves more wasted weekends than anything else I teach.

Algae: the green species

Green algae — the common bloom — answers to the classic protocol: correct the pH, shock hard, brush everything (algae under biofilm laughs at chlorine until the brush breaks the film), and run the filter around the clock, cleaning it as it loads. Most green pools clear in days without draining; the full walkthrough is on our green-to-clean page.

Mustard algae — the yellow dust that reappears on shaded walls days after you "fixed" it — is a tougher strain that shrugs off normal chlorine levels. It needs aggressive brushing, a heavier shock than feels reasonable, and here's the step everyone skips: it colonizes everything — brushes, poles, floats, swimsuits. Rehab the equipment in the shocked pool or it re-seeds the moment you're done.

Black algae — the dark spots that feel raised and won't brush off — roots into plaster pores. Honest talk: widespread black algae in old plaster is usually a sign the finish itself is porous and near end-of-life. You can fight spots with a stainless brush and stain treatments, but if it keeps spreading, the real fix conversation is a replaster.

Stains: organic vs. metal

Organic stains — the tea-colored shadows where leaves sat all winter — mostly bleach out. Chlorine held against the stain (a tablet, or granular in a sock laid on the spot) plus patience does it. The prevention is unglamorous: get debris off the floor before it marinates. Fall leaves left until February will leave their signature.

Metal stains — rust-browns (iron) and blue-green-blacks (copper) — work opposite to instinct: chlorine sets them harder. The play is an ascorbic-acid treatment to lift the stain, then a metal sequestrant to keep the dissolved metal from redepositing, then finding the source — well-water top-offs, corroding equipment, or copper algaecides. Skip the source-hunt and the stain returns like a bad sequel. (Related: if your water itself has a clear green or brown tint, that's dissolved metal too — covered in the water color guide.)

And sometimes: it's the finish, not the filth

The hardest honest conversation: on plaster that's 12–15 years old, rough, and thin, stains penetrate where they never would have in year five — and they don't come out, because the surface itself is failing. At that point stain treatments are rent, not a cure. The signs are all in the renovation checklist, and the fix makes the pool look better than any scrubbing ever could.

Fighting something you can't identify? Our techs see every species weekly — call 713.462.0762 or get a quote, tell us what you're looking at, and we'll tell you the right play before you spend another Saturday on the wrong one.