i think, respectfully, BPs use water features when provided, more often than people may think because my personal observations is that my BP uses it as much as my Afrock and both divide their time in half between swimming/soaking and exploring/sitting - this being said i don’t think you need much depth so space could be saved this way - i would personally consider using something other than the fish tank to accomplish this - at present i use a lot of pyrex glass bowls which are aesthetically pleasing, durable and cheaply available at Walmart