The damaged leaves may not recover completely, but you know you’re in the clear when you stop seeing symptoms on new leaves. You're doing the right thing by not doing any feeding until the ph is corrected because this is more than likely the cause for the deficiency, try to keep the ph between 6.0-6.5, but it could also be the RO water, zinc deficiencies are more likely to appear when a grower is using heavily filtered or reverse osmosis (RO) water to feed plants since any zinc has been removed, but pH is a much more common reason growers see zinc deficiencies in their cannabis plants.