Floaters in a low-tech tank: friend, foe, and the frogbit question
Every low-tech tank thread eventually argues about floaters, usually by people who have kept exactly one species for exactly one month. After a year of frogbit, water lettuce, and a duckweed incident I still have nightmares about, here is the honest ledger.
What floaters actually do
Three things, all real. They eat nitrate faster than any submerged plant per gram of biomass — a frogbit raft is a nitrate sponge with a root system that doubles as shrimp nursery. They shade, which in a low-tech tank is often the difference between "slow growth" and "algae farm." And they signal: leaves going pale and small at the surface is the earliest warning you get that the water column ran out of something, weeks before a submerged plant shows it.
What they cost
Shade is a cost, not just a benefit. The crypts under my frogbit raft grew half-speed and lost their red until I ring-fenced half the surface with a simple air-line loop. That is the whole management technique, by the way: an airline ring, moved whenever I get lazy about culling. Under the ring the Hydrocotyle gets full light; outside it the floaters do their job.
The frogbit question
Frogbit vs water lettuce is a personality question. Frogbit grows in tidy rosettes, culls easy, and explodes politely. Water lettuce is prettier from above, melts badly after shipping, and files a formal complaint every time your lid drips. Duckweed is neither — duckweed is a lifestyle you cannot leave. It rode in on a farm bundle in 2024 and I still find leaves in the filter sock after clearing the tank twice.
The culling discipline
The rule that keeps floaters from running the tank: scoop a fixed amount out weekly, by hand, on the same day as the water change. The "finger scoop" — drag your finger through the raft, lift everything that sticks to it, feed it to the garden — takes thirty seconds and replaces every argument about whether floaters "are too much." If you skip it for three weeks, the raft shades the tank, the crypts stall, and you will blame something else.
Verdict
Frogbit, ring-fenced, culled weekly: net positive. Water lettuce: fine if you have a lid you love. Duckweed: only if you enjoy losing.
The roots, for what it is worth, are where a third of the shrimp colony shrimplets live their first month — the fertilizing schedule assumes they are there.