Question about gravel.

I would vacuum every time you change the water and I see no reason to stop at 22% unless you are buying RO water or have a water shortage. I do 50% water changes every time, 2 to 4 times a month. My frequency of water changes is based on bio-load. I understock most of my tanks. The nice thing about a 50% changes is that you are cutting waste levels in half assuming that your water source is 0.

how big is the tank and what are the current filters?

What about the filters? How often/ how do you clean them? That depends on your filter type, but generally, I do my w/cs weekly 30-50% depending on tank size and bioload. I sqeeze/rinse any filter media in tank water (in a separate container) at least every other water change. I make sure to clean the whole filter (impellers, impeller chambers, inside of filter walls, hoses, etc) every month. I change the fine filter floss completely when it's so super dirty that I can't rinse it clean or every 6 months). I swap out 1/3 of bio media once a year. I don't use chemical filtration, but if you do, you will replace this once a month. Basically, a quick guide for most filter types.

**make sure not to rinse any filter media in tap water!!!!! Keep your beneficial bacteria going. Don't swap out more than one media at a time.