Pufferpunk wrote:??? I am very good about matching the temp, which would be the only difference between the new water & present water in the tank.short periods of ammonia spikes
Your biofilter is off. For that short period of 10 mins there is a small spike while the water is lowering and before it is filling. For the sake of argument the last 20%. During that period the fish is at its most stressed moments. The last, 20% before and 20% after. During that phase there is no filter or equilibrium to balance the equation. During the last 10% of the draw that is when water is at its most toxic. You have an active fish, possibly in panic, and that is when the spike occurs.
Without seeing HOW you do the change, that is a typical scenario. Without adding new water to balance out the old, during the change, the equilibrium is off. As the water decreased the pollutants increase and vice versa. This is only if the fish is under stress aka panic mode. If it is not and relaxed the levels will not change too much.
I don't know how to explain this, but it is so multi-faceted that it is incredible. Water changes are not as simple as swapping buckets. Too much too quickly is bad. Too little too long is bad. You will find a rhythm in the testing.
My mother has a GF in a tiny aquarium (way over stocked) for over 5 years. Stability is the key. Keep it constant. Regular maintenance, regular water changes. Nothing extreme. Your GF is ill, I can understand that. You want to keep the water at its best. But I feel that too much change too quickly is in fact causing stress.