Why animals drink less from a dirty trough
Livestock and horses are conservative drinkers: they take in noticeably less from water that tastes of algae, slime or droppings, and a marginal drop in intake shows up in milk, condition and work long before anyone connects it to the trough. The green film is only the visible part. The slippery layer on the walls is a biofilm of bacteria and organic matter that taints every refill poured over it, which is why tipping out and topping up never really freshens a trough. Animals with no alternative will drink enough to survive from a neglected trough while quietly under-drinking every single day.
The scrub routine, trough by trough
Work one trough at a time so no field is left without water while you clean. Bail or tip the old water out away from the gateway where it would make mud, then scrub every surface with a stiff brush, paying attention to the waterline, the corners and around the ballcock cover where slime is thickest. Scrub until the surface feels squeaky rather than slippery under the brush; that change of feel is the biofilm actually leaving. Rinse the loosened muck away completely and refill. If a trough has been neglected for a long stretch, expect to repeat the scrub after the first refill has been in an hour, because loosened algae keeps flaking off the walls.
Drinkers and poultry waterers need their own routine
Automatic drinkers serving stables and cubicles foul differently: feed and bedding get nosed into the bowl, and the mechanism itself needs a check. Lift the lid, clear debris from around the float, confirm the bowl refills briskly when you press the paddle or empty it, and scrub the bowl's waterline. Poultry drinkers are the highest-maintenance water on the farm, because hens backwash feed and dust into them constantly. Rinse and refill them daily, scrub the drinking channel where the slime ring forms, and raise them to back height on bricks or a stand so litter is scratched in less. A spare set of drinkers rotating through a proper wash makes this far easier than scrubbing the only set while the flock waits.
Siting and season change the schedule
A trough standing in full sun in high summer can need scrubbing twice as often as the same trough in a shaded corner in spring, because warmth and light are exactly what algae wants. Where you have a choice, site troughs in shade and away from overhanging trees that drop leaves into them. In a heatwave, add a midweek check for mosquito larvae wriggling at the surface and for the floating crust of algae that can form almost overnight. In frosty spells the job turns to breaking ice and checking ballcocks have not frozen, but the scrubbing rhythm continues underneath; winter slime is slower, not absent.
Put the round on a rota, and watch the drinkers
The most reliable system is a named person doing a fixed round: every trough and drinker visited daily for a look and a top-up, scrubbed on the set day for that field or shed, with anything odd written down. That oddity log matters, because a trough that is suddenly always full while others empty can be the first sign of a sick animal not drinking, and a drinker found dry points to a stuck float before it points to thirsty stock. Recording the round in KinsLe's Care Teams, with each water point ticked off and problems flagged as they are found, turns water from an assumption into a checked fact on your farm.