pleco trading

If your doing it for the love of plecos, you should have them in an appropriate sized tnak, and doing a better water change routine. Give them an environment they can thrive in, not just survive in.

I agree, get a larger tank and some plecos that stay an appropriate size, then you won't have to return them after two years. I have a blue phantom in my 55, it stays 6 inches max and is awesome! I'm hoping to get a butterfly soon. There are plenty of awesome plecos that stay small(er), there's really no reason to get a common you have to return in a year so it becomes someone else's problem.
 
yes, I've been doing water changes only a couple weeks, but the water has been low, so realistically there's been a 35-45% water change weekly.
When water evaporates, the toxins do not, they stay in the tank and increase in strength (because they are not diluted as much) as the water level goes down. So you are not really doing a 35% water change even though you add 35% by volume to the tank. If you removed 35% of the "remaining water" before topping it off, then you would be removing 35% of the toxins for an effective 35% water change.:)
 
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