I would NOT want to use Bar Keeper's Friend (BKF) in my pool or in such a way that it can get into the pool. The active ingredient in BKF is oxalic acid (it also contains detergents and fine silica grit for polishing). Oxalic acid will help remove water stains, as well as iron stains, from metal surfaces (it works great on stainless steel pans), but oxalic acid is TOXIC upon ingestion. In high enough concentrations, it can cause organ failure, specifically kidney failure. Oxalic acid will form calcium oxalate crystals in your kidneys. Calcium oxalate crystals look like sharp spikes and cause physical damage to the kidneys. Calcium oxalate is the primary component of kidney stones and this is one reason why they are excruciating to pass when you develop them. Chlorine degrades oxalic acid into carbon dioxide, water and chloride ion, so it won't build up in your water but it will create some chlorine demand.
Now, while scrubbing some tiles carefully with BKF is probably not going to add a harmful concentration of oxalic acid to your pool water, you have to ask yourself - why would I want to add something that is potentially harmful to the water when there is an alternative that works just fine, aka, muriatic acid. The answer is, you should not. So leave the BKF for what is was intended for (showers, sinks, pots & pans) and use something else in your pool.
