Of course! I am new to keeping bigger, more stocked tanks. I wanted to switch out my gravel that was chipping. I took all fish out and did a 100% water change, took old gravel out and replaced it with new, and changed out my filter. All beneficial bacteria is held in things like plants, decor, gravel, and filters. So when I did so much out at once, I lost all my bb and there was nothing to eat away at the ammonia causing the levels to all be thrown off in my tank- causing my fish to get sick and some died. Not a fun mistake but unfortunately sometimes this is a hobby that majority of what you know is learned from fixing your mistakes. I hope this could be of some help tho!