Hair Algae, Handled

Know your enemy, briefly

Hair algae, string algae, thread algae, blanket weed, all names for the same idea: filamentous green algae that grows in long strands instead of a flat film. It shows up when two things are oversupplied at the same time, light and nutrients. Strong direct sun plus fish waste and uneaten food is the whole recipe, which is why outdoor tubs in early summer are its favorite place on earth. It is not toxic, but left alone it can tangle fry and small fish, smother plants, mat the surface, and drain oxygen overnight, and it steals the show from the animals you actually wanted to look at.

Step one: twirl it out

No bottled product beats simple manual removal. Take an old toothbrush, a bottle brush, or a rough stick, push it into the mat, and twirl. Hair algae winds onto a rough surface like spaghetti onto a fork, and you can lift a startling amount in one go. Do it every few days and you stay ahead of it, each removal takes the algae's stored nutrients out of the water with it, which is a nutrient export the algae cannot undo. Toss the haul in the garden, it is genuinely good compost. Check the strands for hitchhiking fry before it leaves the net if your fish have been spawning, eggs stick to algae as happily as they stick to a mop.

Step two: fix why it grew

Removal without fixing the cause is a subscription. Break the light-plus-nutrients pairing from both ends:

Cut the light. If the tub sits in six or more hours of direct summer sun, give it afternoon shade, a shade cloth, a repositioned pot, or best of all, floating plants. A healthy raft of floaters shades the water column and dims the algae's grow light all day, every day. Indoors, shorten the photoperiod to six to eight hours.

Cut off its food supply. Feed a little less, medaka in a green, established container are grazing all day anyway, and every pellet you skip is nitrogen the algae never sees. Do a partial water change to drop the current nutrient load. And put plants to work: floaters and fast growers like hornwort eat the same nutrients hair algae wants, straight from the water column. A well-planted tub quietly starves the algae year-round, which is the entire philosophy of my floating plant guide.

The other kinds of green

Film algae, the soft coat on walls and hardscape, is normal, harmless, and the easiest of all: wipe the viewing side, let the rest live, your snails and fry graze it. Brown diatoms, the dusty tan coating on new setups, show up in the first weeks and leave on their own as a container matures; snails eat them happily in the meantime. Green water, where the water itself turns pea-soup, is its own phenomenon with its own fixes, and some breeders culture it on purpose for fry, my green water guide has that whole story. Black beard algae, stiff dark tufts on edges and slow-growing leaves, is a red alga and rare in medaka tubs; trim the affected leaves, keep conditions steady, and be patient, it retreats slowly.

Why I skip algaecide

Bottled algae killers and live animals are a bad pairing, and not only for the obvious reason. When an algaecide works, the whole mass dies at once and starts to rot, and that decomposition can strip the oxygen out of a tub overnight. Keepers lose fish to the cure far more often than to the algae. Manual removal plus fixing the light and the nutrients is slower, and it is the version where nothing gambles with your animals' water.

Where the cleanup crew fits

Now the fine print on the snail pitch. Snails are grazers, not mowers: no snail reliably chews through an established mat of string algae, and anyone who tells you otherwise is selling snails. What snails actually do is patrol, they keep walls, plants, and hardscape cropped of the film and diatoms that outbreaks build from, day and night, for years. Pair them with the light and nutrient fixes above and a tub tends to stay in the balanced, lightly green state where hair algae never gets its foothold back. My snail care guide covers keeping them thriving.