I'm afraid neither of those options will CURE ich. Metroplex food as stated is more geared towards internal parasites as it hits them directly in the gut. When dosed in the water it has anti-microbial properties. Crypto does not seem effected.
The Dr. Gs food has CP, but it's not specific on dosage for each individual fish. You don't know how much each fish should consume to receive a therapeutic dose. In humans, this is determined partially by the weight of the patient (children vs adults, etc)
So if your one fish only nibbles the food and another gobbles it, and one fish is tiny and one is a whopping 7 inches...it could make a difference in how effective it is. When we dose the water correctly, the entire surface of the fish and all around it is a consistent, therapeutic level. And ich and velvet are External parasites, so this is more effective regardless. The CP or copper does not kill them on the fish, but rather disrupts their lifecycle after they emerge from the encysted stage.
For ich management, regular water changes including vacuuming your sand bed, using a UV sterilizer, and feeding high-quality, vitamin-enhanced foods are some frequently suggested tactics.
I know it's frustrating, and I wish you luck regardless of how you choose to tackle it.