Can you put too much dechlorinator in your fish tank?

With Fritz Complete, you can treat extremely high levels of chloramine, nitrite, or other toxic chemicals by dosing up to 5 times the recommended amount within the span of 24 hours. This is a very large range that allows much room for error. Just keep in mind that potent concentrations of dechlorinator will quickly reduce the amount of dissolved oxygen, so it may be best to add an air stone for the next 3-4 hours to increase oxygenation in the water.

For more information, read the full article on dechlorinators.