Oh dear! Last summer?
Problem with that kind of tank maintenance is you'll have a case of Old Tank Syndrome.
If you tried to right things (I imagine the nitrates must be sky high) the fish would be shocked by clean water.
most pet stores use strips which cannot be relied upon
although I agree the stock isn't bad, water changes also replenish much needed vitamins and essentials for the tank....can you imagine living in your bathroom without ever flushing the toilet? LOL that's what no water changes remind me of ....but I agree...doing too much of a change with them, could give them a major shock....id go with maybe 10-20% changes every other week at least...just because they survive, doesn't mean they are striving....would love to see pics sometime! I love the hex tanks
The place I take them to uses a full test kit, and are really accurate (they must be to have 5 show tanks one with discus). And I wouldn't really say its a LFS. Its called the Dallas North Aquaruim. With the tank, would it help that it is heavily planted????? The neon tetras in there are doing a ton better in it then in my bowfront (46 gallon; they are surviviours from my bad choice of madagascars with them. They were alone for a while.) Heres a pick.
The heavy planting does help. But water changes and gravel vacs do more than get rid of nitrates. They get rid of debris, put oxygen into the water, replenish necessary minerals, and make it so that dangerous gas pockets don't build up in the substrate.
But really, I agree with the others. The fish are probably so used to those conditions that sudden large water changes (I do 50-60% weekly) would kill them.