erm. sorry im beginner in rearing marimo. when i wash it, there are some little patch of my marimo came off.. is it normal or i squeezed it too hard? :/

Thanks.. Because Ive bought it from a pet shop and the sales assistant there says no need to squeeze the marimo to clean it but just change the water and after that i found out in the net that it is a need. So, I assume they did not clean it for a long period of time :/.. Poor marimo, this is because, the water became dirty easily when i first bought .. so i kept on changing the water