Start with the water your fish will actually live in
The most important question is also the one most owners never ask: whose water will the fish be swimming in? Many shops board fish in their centralised shop system, where one filtration loop serves rows of tanks. That water is kept to the shop's parameters, not your tank's, and a fish from a soft, acidic home aquarium dropped into harder, more alkaline shop water is being asked to adjust its whole body chemistry on arrival — and then adjust back when it comes home. Ask whether boarders can be kept in a separate tank, how the shop's temperature and water chemistry compare with the readings you bring from home, and how they acclimate fish in and out. A good shop asks you for your parameters before you finish asking them for theirs.
Ask what happens when a fish gets sick
Boarding concentrates fish from many homes in one place, which is exactly why the illness questions matter. Is there a quarantine or hospital tank, and are newly arrived boarders held apart from fish already in residence? If one of your fish develops white spots, fungus or a bacterial problem mid-stay, what precisely happens: do they treat it, isolate it, phone you first, and at whose cost? What if a fish dies in their care — an honest shop has a plain answer and a policy for telling you, rather than a shrug at collection. Also ask the reverse: do they refuse boarding to fish showing symptoms on arrival? A shop that inspects incoming boarders is protecting your fish as much as its own stock.
Pin down the daily care in specifics
Vague reassurance feeds no fish. Ask what food they will be given — and whether you can supply your own, labelled, if your fish are fussy or on a particular diet — how often feeding happens, and whether anyone checks each boarder individually every day. Staffing is the quiet deal-breaker: who feeds and checks the boarding tanks on Sundays, on bank holidays, and during the shop's own busiest sale weekends, and is the building alarmed and temperature-controlled overnight? If a filter serving the boarding tanks fails at midnight, whose phone rings? Shops that board well have thought about these hours; shops that board as an afterthought reveal themselves by having to invent the answers.
Settle the practical terms before the fish leaves home
Finish with the unglamorous list. Which species and sizes do they accept, and are there fish they will not take? What is the full cost for your actual dates, including any charge for treatment or extended stays if your return is delayed? What must you bring — the fish bagged how, any water sample, your parameters written down? And what happens at collection: will they bag the fish in water matched to your home tank's readings, and is there a day or two of grace if your flight home is cancelled? Write the agreed answers into the booking note, and if you found the shop through the KinsLe Pet Services Directory, keep the conversation there so the questions, the answers and the booking live in one thread you can both look back at.