Advice given needs to be to the level of understanding and capability of the OP. Judging by the content of his posts I would say a 100% water change is a bad idea.
Yes, most all capable, experienced fish keepers know that 100% WCs can be done safely with little risk.
Bic lighters are safe, but I wouldn't allow a 4 year old to use one.
Yes, most all capable, experienced fish keepers know that 100% WCs can be done safely with little risk.
Bic lighters are safe, but I wouldn't allow a 4 year old to use one.

