Small invertebrates arrive quietly and cause arguments later. A snail species multiplies, shrimp fade over a fortnight, or a parasite appears, and without a written line for each batch you are left blaming the whole collection. A batch log turns suspicion into a short list of suspects with dates attached.
One line per batch, six fields every time
Fill in the line on arrival day, before the bag is even opened where you can. Give every line the same six fields: the date, the species, the number added, the shop, the destination tank and an observation covering the following 14 days. Name the species as precisely as the shop named it, and where a shrimp grade or snail species is easy to confuse later, write the distinguishing colour or pattern beside the species name inside that same species field. Count what actually goes into the water, not what the bag was supposed to hold, because a short count written down beats a wrong count remembered. One batch split across two tanks gets two lines, one per tank, so a problem in a single tank points at a single line.
The 14 days after arrival
Complete the observation field across the following 14 days rather than in one sitting. Note deaths there as numbers and dates, odd behaviour such as shrimp sitting motionless in the open, snails staying shut for days, empty shells, or animals that simply stop appearing. A batch that settles, feeds and moults normally earns a short line saying so, and that quiet line matters later because it clears the batch when trouble starts elsewhere. Resist tidying the log afterwards. A corrected memory helps nobody, so add a fresh note inside the observation field with its own date when new information appears.
Working backwards from a problem
Start from the date the problem showed itself, then read upwards through the lines for that tank. Batches whose 14-day observation closed before the trouble began, with normal behaviour recorded, move down the suspect list. A batch still inside its 14 days, or one whose observation already holds early deaths, moves to the top. Check whether other tanks received animals from the same shop on nearby dates and whether their lines stayed clean, because that comparison separates a shop-level problem from a tank-level one such as water quality. Keep the suspect lines unedited while you investigate, because an altered observation cannot be trusted by you or by the shop. Test the tank water before blaming any batch, since a log that ignores a filter fault will accuse innocent stock.
Talking to the shop with dates in hand
Contact the shop for the suspect line and give them the date, the species, the number added and what the observation field recorded. Shops that hear a calm, dated account can check their own tanks and other customers' reports, and many keep delivery records that match yours. Your log also protects a good shop, because it may show the losses began before that batch arrived. If the shop asks for a water sample, take it from the destination tank named on the line that same day, and label the sample with that tank's name and the batch date so the result stays tied to the right line. Either way, the answer comes from evidence rather than from whoever feels blamed.
KinsLe's Pet Passport can hold each tank's batch lines in date order with the rest of its records, so the evidence for any problem sits in one packet when you need to trace it.