changing substrate

Hi guys this is my first post here so idk if im doing anything wrong or not but anyway, I have just plain old gravel and i wanted to switch to eco complete but i am unsure how. i know that a lot of bacteria live in the substrate and getting rid of it can cause a mini cycle, which i want to...

I have a mix of gravel and original Flourite in my 55 gallon that I have been wanting to switch out for a long time. 15 years ago I started it with gravel and then about 10 years ago I took out half and mixed in half Flourite. Gravel and Flourite doesn't look good imo. I'm now planning to...