never had water changes but only water added as it evaporated
We can follow what happens in my tanks.
While I do not follow the 'never' water changes, sometimes I do go for a while with only topping off. Lets just follow the TDS (Total Dissolved Solids)
TDS = upper 200s, usually between 250-280
Tank, right after a water change (assume 100%) is matching the tap water.
Some water evaporates, but it does not take the minerals with it. I add more tap water (and therefore more minerals). The plants are using a very small amount of these minerals. Not enough to really drop the levels.
Over a week or a month the amount is not much, and a big water change (50%) would reset it to match (or nearly match) the tap with no strain on the fish.
Over several months it keeps adding up, though.
By the end of the summer the lowest TDS I can find in any tank is in the upper 300s, pretty close to 400. Most tanks are well into the 400s. Basically it has doubled.
In actual fact I am doing very small water changes. I am taking out enough water to clean the filters, perhaps once a month. A couple of gallons cleans most filters. This is easily 20% on the smaller tanks, but not even 10% on the larger tanks. And the TDS is climbing...
The GH is rising, too. The KH is different because I have some substrates that remove it. I am not replacing enough water to keep the KH up. So it drops, and this allows the pH to drop.
To do larger water changes get away from the buckets.
I have several garbage cans. When I was doing 50% per week, every week on about 20 tanks I would fill the garbage cans with whatever water I needed (Tanks had different water chemistries from black water & RO to low end brackish) and use pumps.
A siphon (gravel vac) to get the water out into a bin on the floor. Clean the filter in that. Keep siphoning more water out of the tank. Pump and garden hose got the dirty water out to the garden.
New water added to the tank from the garbage can via pump.