Siphon Suction Wont Work

If you've got soil in the tank, it could be that big water changes are counter productive as it disturbs the soil and releases nutrients into the water. What measurements are you taking? If you get your plants thriving, they will make your water is pristine. My experience from setting up my planted tank is that the nutrients that impeded plant health weren't obvious. What are the nitrate readings for your tank - before and after water changes?

I'd just add to what Richard has said in that you don't really want nitrate levels that are too low as your plants will suffer for it.

I think I might have replied to that thread as well.

The problem with this would be if the bin end of the second siphon tube was lower than the windowsill. Then it wouldn't siphon using a plain tube, you'd have to pump it out of the bin.

We do water changes for other chemicals as well, ones we can't measure. But nitrate levels are used as a guideline for all the others. If nitrate is going up, so is everything else; if nitrate stays low, so does everything else. Unless your tank is a jungle when the plants will remove a lot of nitrate but maybe not the other things.

In AM's case, she doesn't have many fish yet so big frequent water changes aren't needed.