Since this toner contains PHA, PHA is the gentlest exfoliating acids among BHA and AHA, I definitely wouldnβt want to use 2 different exfoliating acid products in one day(I mean one day, 2 routines morning and night), I do think we are not professional and it would be best to not mixed two different exfoliating product at once unless itβs a two in one kind of exfoliating product.
If I were you, since you are not a newbie in exfoliating acid products and these acids does appears in your normal routine, I would temporary stopped all the exfoliating acid products you normally would use, and stick to this PHA toner to give a fair chance to really test out the product, plus your normal routine already include a slight stronger/ much high chance irritating exfoliating acids such as BHA and AHA, PHA is the gentlest among them hence you might not really see the result.
To be safe, I would slowly introduce this PHA toner into my routine too, possibly try it 3 times per week and pay attention whether anything unusual happened and slowly increase the frequency of using it to daily basis just in case your skin needs time to adjust in using this PHA toner.
At the same time, while using this PHA toner, it would be best to stopped all active ingredients your normal routine would have, just stick to this PHA toner and serum/ essence and moisturiser with soothing and hydrating effect.