If you do something without having to think about it, that might be instinct. The more you think about it, unless you ultimately go with your “gut” anyway, it is probably intelligence. Even going with your gut might be intelligence. Your brain can subconsciously figure out a lot of variables...
Beneficial bacteria grows in places oxygen can get to. That’s another reason for vacuuming the gravel. It stirs up the gravel as well as removing muck so you don’t have unoxygenated areas that grow gram negative (bad) bacteria. Enough bacteria sticks to the sand or gravel to keep the cycle...
In plain English, I vacuum gravel to the glass and swirl just over sand to get detritus on the surface. Things fall in between the gravel and get to the bottom. Some stuff they sell as sand is large like small gravel and not like beach sand. I vacuum that to the glass bottom. If it is fine sand...
They look like endler/guppy mutts to me. The one on the right looks like it has some tiger endler and maybe Japanese blue endler(?). The one on the left has some guppy but might be crossed with endlers too.
Editing to add that @emeraldking is the expert on these, so I am just giving my opinion...
That T in a box allows you to add text. Then you click any where on the page and start typing, hit enter when you want it to drop down to the next line. Then you can move the box where you want it, too.