Concrete pots leach lime - turns the potting mix extremely alkaline. I think based on DIY hypertufa pot guides on the web (they say this is a must for new pots - I think it's also a necessity for old pots but thorough cleaning would be required first!) is to soak the pot in water for at least two weeks (completely submerged, change water at least once daily) then let it dry out then apply two to three coats of concrete sealer.
I usually add a bottle of vinegar to the water on the 4th and 8th day (so if you change water daily, then that means the pot would have had 2 vinegar water soaks) - doesn't matter how large or small the bottle is, as long as you mix in some vinegar in during the soak and rinse process.
I use my hypertufa pots on ornamental succulents only though and sanseverias so YMMV - not sure what other plants wouldn't mind being rehomed in concrete pots.
EDIT: I realised if your pot is too large to fit in any rubbermaid tote or even an IBC, perhaps using pond membrane as liners to at least insulate the roots and keep them away from the concrete would be more economical/practical?
