Disclosed is an in place cleaning method, the method comprising the steps of (a) treating the foulant with an acidic solution to remove metal ions from the foulant and (b) basifying the acidic solution thereby contacting the treated foulant with a basic solution to remove at least some of the treated foulant wherein the acidic solution and/or the basic solution comprise at least one chelant in an amount sufficient to stabilise metal ions in the basic solution.
