The Bloon Solver is the final upgrade of Path 1 for the Glue Gunner in BTD6. It allows the glue fired to dissolve Ceramic and M.O.A.B. Class Bloons three times as fast. It also allows the Glue Gunner to fire 4x faster, along with gaining a powerful Glue Splatter that allows it to hit up to 12 bloons, 16 with Glue Splatter and 18 with Splatty Glue. It costs $20,400 on Easy, $24,000 on Medium, $25,920 on Hard, and $28,800 on Impoppable.
It is recommended to buy the 5-0-2 Glue Gunner instead of the 5-2-0 Glue Gunner because The Bloon Solver shoots quickly and comes with a free glue splatter. The Bloon Solver will glue many bloons in its path already, so making its glue last longer is a more worthwhile asset than just to allow it to glue only 4 extra bloons per shot.
It is best to place The Bloon Solver near the exit, though not directly at the exit. This will help provide time for the liquefying glue solution to corrode any surviving weakish bloons.
There are several significant advantages of using The Bloon Solver to defeat Super Ceramics instead of The Biggest One. Provided it is placed in a good spot near the exit, The Bloon Solver can handle Super Ceramics with ease without requiring any micromanagement. Additionally, the damage-over-time allows The Bloon Solver to single-handedly eliminate affected bloons with a single glue attack. Finally, it's also cheaper (one 5/0/2 Bloon Solver costs $38,440 on Hard Mode, while a 5/2/0 Biggest One costs $43,095 on Hard).
Deals more damage to Ceramics and MOAB-class (2 --> 3; essentially 3x faster than Bloon Liquefier's damage rate)
The artwork shows that the tank on the monkey's back is not a glue container. It is believed to be an oxygen tank as its pipes are connected to its mouthpiece not the gun and it has glue containers on the gun. This shows that the fumes of the super corrosive glue are so toxic that they can't even be breathed with a gas mask and the monkey constantly needs to breathe from an oxygen tank.
The in-game description puns on the fact that the way of fixing the problem of bloons is solved as well as the fact that the problem is solved with a chemical solution.
Despite popular knowledge, The Bloon Solver actually corrodes bloons below Ceramic at the same rate as Bloon Liquefier.