>>2947816
There is also a powder. You get more in the powder but the gel is better as it adheres to toilet bowls and "sloped areas" better. The powder is good for toilet reservoirs/basins though. Powder is more expensive but only by $1-2 but you get more as mentioned.

There is also a lime scale remover by them too. called Limeout
Lime Out Heavy-Duty Rust, Lime & Calcium Stain Remover, 709-mL It's about the same price as the gel rust remover.

You'll have to decide which product to use on that though as you need to figure out if it's lime scale or rust and buy the appropriate product.

Note, it smells pretty nasty so don't breathe in the fumes directly but just let it do it's thing. Works well and fast too.