I'd simply avoid messing with your PH then, Bettas like soft water (i think) and there is more likely to be problems changing your PH than not changing your PH.
Simplest example; If your PH is around 5.5 atm then adding this (wardleys) could actually result in a spike anyway, beneath ph5.5 ammonia ceases to be toxic (ammonium), raising the PH quickly (with the aforementioned product) would allow ammonia in its toxic state to develop while your A.O.B and N.O.B (cycling bacteria) would have died off. Similar to the causes of OTS (Old Tank Syndrome).
If anything i'd go for SeaChem Prime, IMO as well as many other aquarists and fish shops this is the best Dechlor going.
It successfully detoxifies ammonia, nitrite, nitrate and also removes chlorine and chloramine.
While you only get a small bottle for your money, the amount needed compared to many Dechlors is tiny and it is actually one of the cheapest Dechlorinators going, anyhoo.....
That answer was a bit over the top, basically don't bother with the Wardleys.