Why the gravel vacuum is the wrong tool here
A standard gravel vacuum is built to move a lot of water quickly, and that strength works against you in a fry tank. The bore is wide, the pull is strong, and a days-old fry weighs almost nothing and swims weakly, so a baby that wanders near the intake has no chance of fighting the current. Fry tanks also tend to be bare-bottomed, which concentrates the problem: every scrap of uneaten food and waste sits visibly on the glass where the fry rest, and because fry are fed little and often, that layer builds up faster than in an adult tank. Left in place it feeds ammonia exactly where the smallest fish spend their time, so the floor does need cleaning — it just needs a slower tool.
The airline siphon, pass by pass
Airline tubing is the classic answer because its narrow bore can only move a thin stream of water. Start the siphon in the usual way and let it drain into your bucket; to slow or stop the flow, pinch the tube or lift a kink into it rather than pulling the end out of the tank. Hold the intake a few millimetres above the floor and sweep it slowly along, letting the gentle current lift waste toward the opening while fry simply drift aside. Work one strip of floor at a time, and pause whenever a cluster of babies investigates the tube — curiosity is normal, and a paused siphon gives them time to wander off. If your fry tank has a corner where waste collects, aim your passes there rather than stirring the whole floor in one session.
Drain into a pale bucket, and check it like it matters
Even with a slow siphon, the odd fry will occasionally ride along, so the bucket is your safety net. Use a white or pale container, because a two-millimetre fry is nearly invisible against dark plastic but shows up clearly against a light background. When you finish a pass, let the bucket settle, hold it to the light, and scan slowly. Any stowaway can be lifted out with a pipette, a turkey baster used gently, or a soft fine net, and returned straight to the tank. Never tip the bucket away on autopilot — the thirty seconds spent checking is the entire point of the method, and on a bad day it is the difference between a clean floor and a lost half-batch.
Little and often beats one big rescue
The safest fry-tank cleans are boring ones. A short pass every day or two removes waste before it compacts, keeps each water change small, and never asks you to hurry around dozens of babies with a running siphon. Top the tank back up with conditioned water matched to the fry tank's temperature, dripped or poured in slowly so the level rises without a current. If you find yourself rescuing fry from the bucket every time, slow the siphon further, clean before a feed while the batch is spread out and calm rather than swarming, and shorten the passes again. Keeping these small cleans on a visible rota matters more than technique alone, and KinsLe's Care Teams lets you set the fry floor clean as a recurring duty whose completion is marked each time it is done.