There's a bit of a contradiction in the advice appearing here.
You are looking for optimal temperatures for health, and growing is part of healthy development for any fish. To intentionally stunt it through underfeeding strategies is to mistreat the fish, and will lead to ill health. Keeping it in a 33 gallon, or even six in a 125 may be a short term adventure.
When I made the mistake of trying to keep this fish many years ago, growth in the first year I had them was fast. I had three of them in a 3 foot tank, so there was no complete second year. They grew, and crashed. I would say they went from 2 inches at the store to about 5-6 inches at death.
They were one of my biggest regrets, as far as things I bought I should not have. I tried everything to save them except the most important thing - a way bigger tank with higher levels of water flow. In the 30 or so years since then, I've seen a lot of clown loach set ups, and spoken to a lot of keepers. As radical and 'out there' as this will sound, I'd probably consider a 180 gallon as basic to six of them with no other tankmates. A 240 would be better. My experience says that in an adequately sized tank on a healthy diet, 5 inches is reasonable after a year. Remember that this is a fish that can be growing without adding total length. They are high backed, and wide bodied, as an all arouned chunky species, and adding body height and bulk is normal growth (and adds a significant bioload).