The stains reappeared because you were not using enough (any?) sequestrant. Ascorbic acid will remove the metals from the pool surface, and puts them back into the water, where they are able to form fresh stains unless you do something to prevent that.
Sequestrant binds to the metals and prevents them from forming stains. However, sequestrant breaks down slowly, so you need to add more regularly.
Metal Free is not one of the sequestrants we recommend using. Sequestrants based on HEDP, phosphonic acid, or phosphonic acid derivatives are the most effective. ProTeam's Metal Magic and Jack's Magic The Pink Stuff (regular), The Blue Stuff (fresh plaster), and The Purple Stuff (salt) are some of the top sequestrants. You can also find many other brands with similar active ingredients, some of which are noticeably less expensive.
It is common for the water to get cloudy after adding sequestrant. This typically lasts one to three days. If it continues longer than that something is going wrong.