Green Pool Cleanup and Algae Removal

Green, cloudy, or dark: what your water is telling you

Bright or pea-soup green water is free-floating green algae, the most common bloom and the easiest to kill once the chlorine is high enough. Cloudy water with a faint green or grey haze is usually an early bloom, dead algae that the filter has not caught yet, or a filter that is not doing its job. A yellow or brown dust that collects in shady corners, brushes away easily, and is back a few days later is what pool pros call mustard algae. Dark blue-green to black spots that stay put under a brush are usually black algae, which tends to build a protective layer and anchor into rough plaster, so a single shock rarely finishes it.

Each one needs a different amount of brushing, chlorine, and patience, so the first thing we do is look closely at the walls, the floor, and the filter before adding anything.

Why chlorine alone sometimes fails

Most green pools in the Houston area are not out of chlorine because nobody added any. They are out because the chlorine could not keep up. Cyanuric acid (stabilizer) shields chlorine from sunlight at a price: it holds part of the chlorine in reserve, so the free chlorine level needed to kill algae climbs along with the stabilizer reading. Chlorine tablets add stabilizer every time they dissolve. After a summer of tablets, stabilizer can climb so high that a normal shock barely makes a dent. When that happens, the only practical fix is replacing part of the water, and we will tell you so instead of pouring in shock that cannot work.

Phosphates are the other hidden factor. Fertilizer runoff, pollen, and decaying leaves carry nutrients that help algae come back, and one major salt system maker lists phosphates among the first things to test when a chlorine generator cannot raise the chlorine level. We test stabilizer and phosphates before we decide on a plan.

What a cleanup actually takes

Killing algae is the short part of the job. Algae dies fast at the right chlorine level, but the dead algae still has to be brushed loose, filtered out, and vacuumed, and the filter will clog more than once along the way. Cartridge filters often need to be pulled and hosed down during the cleanup, and sand or DE filters need repeated backwashing as pressure climbs.

We consider a pool finished when the water is clear to the main drain, the walls and floor show no algae, and the pool holds its chlorine overnight. A pool that is still losing chlorine overnight still has algae somewhere, and stopping early is the usual reason a pool turns green again a week later.

Keeping it from happening again

Houston averages more than 100 days a year at 90 degrees or hotter, and sunlight burns off unprotected chlorine quickly. In that kind of heat, a pool that misses one or two weeks of care can bloom. The most reliable prevention is a steady routine: chlorine held at the right level for your stabilizer, a clean filter, and someone checking the water every week. That is exactly what weekly pool service covers, and starting it right after a cleanup means the first visit begins from clear, balanced water instead of another rescue.

If a storm caused the bloom, start with debris and equipment safety before chemistry; our storm cleanup service covers that order of work. If the filter is the weak link, a deep filter cleaning after the cleanup resets it for the season.

Signs your pool needs a green cleanup

• You cannot see the main drain from the deck
• Water is green, teal, grey, or brown instead of blue
• Walls feel slick or slimy when you brush them
• Yellow dust keeps coming back in the same shady corner
• Dark spots on plaster that a brush will not move
• Chlorine reads zero a day after you shock
• Filter pressure climbs right after a cleaning

What the cleanup includes

• Full water test, including stabilizer and phosphates
• Shock dosed to your stabilizer level, not a guess
• Brushing walls, steps, and floor to break up algae
• Skimming leaves and vacuuming dead algae to waste or filter
• Filter cleaning or backwashing during the cleanup, as often as needed
• Partial drain and refill when stabilizer is too high to treat
• Rebalancing pH, alkalinity, and calcium once the water clears
• A follow-up plan so the pool stays clear