Got the image to load, finally -- Definitely hold off. Some minor blemish on one of the oldest leaves is not something to react to strongly. Worth keeping an eye on it.
Leaves can develop blemishes just from touching or nearly touching the pot or substrate and nothing to do with nutrition. Old leaves get fugly with time. If the plant is not shedding them, they are value-added, no worries.
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6.2 would not hinder Ca. In fact it'd be more available at 6.2 than 5.8. Lower pH generally requires more Ca, which at some will then lockout a ton of other stuff because it's a +2 charge with greater affinity for bonding sites. So, don't overreact either way. If you come to the conclusion it's low Ca, step up slowly. It can take weeks to see the entire reaction to any change in formula. Obviously if it continues to trend poorly, may need another increment. It's easier to add stuff than to take away. Once the plant uptakes too much, it has no excretion system. It's there until it is used or causes damage.