Shorten the trip to the surface
A betta breathes air at the surface and feeds there too, and for an elderly fish that short climb can become the hardest part of the day. Long fins that once looked weightless now drag, muscles tire, and a senior may pause halfway or sink back to a leaf before trying again. The most valuable adjustment is simply distance: rest places near the top, and if the tank is deep, a lower water level that still suits the filter and heater.
Add broad leaves or a smooth resting perch a short swim below the surface, then another partway down, so the betta can climb in stages the way a person uses landings on stairs. Position the topmost rest where the surface above it stays calm and open, not under the filter outflow, so arriving there actually brings rest rather than a fight to stay in place.
Calm the flow without staling the water
An elderly betta resting in current spends the whole day swimming, even when it looks still. Baffle the filter output, turn it toward a wall, or spread it through a spray fitting lowered in force, aiming for water that circulates without pushing the fish's fins sideways as it rests. You will know the adjustment is right when the betta chooses spots away from its shelter voluntarily, rather than wedging itself behind the heater to escape the stream.
Warmth matters alongside calm. Seniors feel a cool tank in their appetite and activity sooner than young fish, so check the heater against a separate thermometer and keep the temperature steady in the range the betta has always lived in. A spare heater kept in the cupboard turns a failure from an emergency into an errand.
Feed where he already waits
Put the food where the fish is. Drop softened morsels one at a time directly above his resting leaf, wait for each to be found, and remove what drifts away uneaten before it fouls the water. An elderly betta with fading aim may need the same piece presented twice, and patience at that moment is worth more than any special food bought in hope.
Keep the feeding spot constant. A senior learns the geography of meals the way he learns his resting places, and moving the target around a rearranged tank costs him meals he cannot spare. If tankmates share his home, feed him first in his corner before the others are given theirs at the far end.
Familiar surroundings, gentle upkeep
Resist redecorating. An old betta maps his tank slowly and relies on that map, so keep his cave, plants, and routes where they are, replacing worn items one at a time. Smooth any rough edges he brushes when turning, since ageing fins tear easily and heal slowly, and keep lighting on a steady, predictable cycle with no sudden full brightness after dark.
Do maintenance in small passes rather than one deep clean, and never strip the tank bare around him. If a move to a smaller, shallower home becomes necessary because he can no longer manage the climb even with rests, move his own plants and water with him so the new tank smells and looks like the old one.
All of that geography only protects him if it survives your busy days, which is why KinsLe stores it in his Pet Passport so the betta's resting spots, flow settings, and feeding corner stay recorded for whoever looks after the tank.