Baquacil is problematic because dealers have end-users rely strictly on blind dosing of the sanitizer and oxidizer without any testing. What we know is that the biguanide sanitizer tends to breakdown slowly enough that the usual dosing keeps it at the right level (at least in pools) but that the recommended level doesn't really seem to be strong enough to protect against bacterial growth. The oxidizer, hydrogen peroxide, is very unstable as there is no easy way to stabilize it against UV and thermal losses and it usually fluctuates all over the place because, once again, people rely on simple time-based dosing rather than measurement to guide dosing. The oxidizer is the only thing that will breakdown bather waste and if it is insufficiently low, then that bather waste is food for the bacteria. Oils and lotions tend to provide the basic lipid materials needed for biofilms to form in the plumbing. Once bacterial biofilms form in the plumbing, you then have a constant, fast-replicating reservoir of bacteria to deal with and the tub must be purged and drained. The spa dealer will try to sell you all sorts of clarifiers and enzymes to deal with the issues but none of those products either works or gets to the root cause of the issue. So you wind up going through the revolving door of poor water quality, spending lots of money to marginally fix it and then slowly returning to poor water quality again. It becomes a major hassle and a major drain on the wallet.
One way to do a better job of dosing and maintaining a baquacil pool is to use a biguanide and peroxide test kit; the strips that vendors provide are all but worthless. Unfortunately the test kit for biguanide and peroxide is quite expensive, about $180 last time I looked. The other issue is that you absolutely can not use any of the Baquacil algaecides or metal controlling chemicals that are sold to users as "fixes" to their problems as those have very strong, positive interference with the biguanide titration test. If those chemicals are present, you'll never get a reliable baquacil reading (it will read off-the-charts high).
Given all that, baquacil sanitized waters are always a lot more work and much more expensive to maintain since the raw chemicals are very pricey. It's certainly your spa and your prerogative to manage it the way you want, but don't be surprised by very poor water quality and expensive "solutions" from the spa dealer to fix it....or more frequent water exchanges.