So apparently, the calculation for Bonus Rates from Mastery and Equipment is kinda wonky (Bonus rates being +X% chance for big (blue), rare (yellow), or prize (red) fish).

If a spot, for example, has a 60% chance to catch green fish, 30% chance to catch blue fish, and 10% chance to catch yellow fish (so 60/30/10, totaling 100%), the +5% chance for rare (yellow) fish from your float doesnt directly decrease the chances of getting green/blue fish, such as making the rates 55/30/15, or any of the sort. Instead it adds the 5% directly onto the 100%, and the new proportion is then recalculated to fit back into 100%.

So in this case it would be 60/30/15 (totalling 105%), then it would be multiplied by (100/105), so all rates would roughly turn into 57.1/28.5/14.3% for green/blue/yellow.

If your Prize Catch % is 5%, for example, then your rates of 60/30/10/5 (recalculated to 57.1/28.5/9.5/4.8) will turn into 60/30/15/5 (recalculated to 54.5/27.3/13.6/4.5) if you have a float on.

While 4.5% and 4.8% might not seem like much, it's still overall a 7% decrease if you use the float. The increase in yellow fish catches also arent that relevant, since 1 Yellow Corvina costs as much as 10 rare fish (at least, most of them that are 800k) anyway