Question: Is using Excel different than if i just turned the bottle up? Arent they basically doing the same thing, adding co2?
The active ingredient of Excel is a toxin, most commonly used as a medical disinfectant.
This toxin is found in small quantities in nature, so all living things have some degree of protection against it. Only when the dosage overwhelms this protection is something harmed.
At normal doses, generally nothing is affected.
At 2-3 times overdose or with spot treatments, it can overwhelm algae's weak protection. Most plants, fish, etc. have better protection and are typically not affected. Though with a much higher dose, you can effectively kill everything in your tank.
Plants protect themselves by breaking it down. In a happy coincidence, one of the breakdown products is CO2. But it's a tiny amount, completely insignificant when compared to what a pressurized or DIY system can provide.