The Smallest Budget in the Room Still Needs Lines
A least killifish is one of the smallest livebearers in the hobby, and a single fish costs very little to keep. A colony, which is what you will have, costs a little more and changes size on its own, so the monthly budget should be written for the colony you expect rather than the handful you bought. Plan for fine powdered food and small live foods, conditioner for gentle partial changes, test supplies, upkeep of dense planting, and a reserve for a second small tank or rehoming supplies if fry outgrow the space. The tracking matters more than the spending here, because population is the moving part.
Food for Fish Measured in Millimetres of Appetite
Adults pick at tiny items all day and newborn fry need food finer still, so budget for powdered fry food, microworms or similar small live cultures, and crushed quality flake as a base. Track what was fed and whether fry are visible and growing after feeding, since a culture that crashes quietly can stall a whole generation before you notice. Note feeding frequency too: little and often suits this species, and a log shows whether that rhythm survived a busy week. If you grow plants or algae for natural grazing, record trims and die-offs, because cover and grazing both shrink when planting thins out.
Water Tracking for a Hardy but Small System
Least killifish tolerate a wide range of conditions, including harder water that many soft-water fish dislike, but a small planted tank still drifts. Log acidity, hardness, ammonia, nitrite, and nitrate on a monthly rhythm, and record each water change with its size and conditioner use. Note temperature swings in an unheated or lightly heated setup, especially near a window, because fry production often pauses when conditions cool and resumes when they warm. That link between temperature notes and fry counts is one of the most useful patterns your record can show, turning a puzzling quiet month into an explained one.
Counting a Colony That Counts Itself Upwards
Once a month, count what you can at feeding time: adults, larger juveniles, and new fry, written as honest estimates if exact numbers hide in the plants. Track the sex balance you observe, because a colony skewing heavily one way behaves differently and breeds differently. Note any fish that look pinched or hollow-bellied among well-fed tankmates, and record removals, gifts to other keepers, or moves to a grow-out tank with dates. Those population notes protect you from the classic livebearer surprise, where a stable-looking tank is suddenly overstocked and water quality starts sliding under the extra load.
Spending Decisions the Log Should Drive
Review the month before buying anything: if fry counts are climbing, next month's real cost may be space, not food, and the budget should shift toward a grow-out setup or planned rehoming. If test results are creeping despite regular changes, the colony has probably outgrown the filtration, which the headcount notes will confirm. If several adults die or fry stop appearing in a previously productive colony, look back for a plant die-off, a missed run of changes, or a new addition, and seek an aquatic veterinarian's input if losses continue. KinsLe's Pet Passport keeps those colony counts and water readings together, so your least killifish record stays portable and readable at a glance.