I'm not a fan of the Formula foods either, but since they're working for you, no sense in changing that up. I'd look into Emerald Entree, it's a great frozen cube food for tangs and dwarf angels.
I prefer that tangs are offered algae sheets EVERY DAY. Naturally, they're grazers and spend all day swimming and grazing, so you want to replicate that as best you can.
If your fish won't take algae sheets right away there are a few things you can try:
1) try different brands and colors. My fish refuse green, doesn't matter what brand. I've had the best luck with Julian Sprungs (Two Little Fishies) algae sheets in purple and Ocean Nutrition algae sheets in purple, red and brown varieties.
2) Rubberband an algae sheet to a piece of live rock rubble. Let it sit in the tank and flow with the natural movement of the water to make it look more like a live piece of seaweed. This will sometimes entice them to try it and once they realize what it is, they'll keep going back and can eventually be converted to the sheet on a clip.
3) Turn off return pumps and leave on powerheads. Take a piece of the sheet and hold it in the water in front of a power head and gently rub it between your fingers to break it apart. It will look like flake food in the water. This method has worked best for me, especially with the Ocean Nutrition algae sheets. My Coral beauty will not, even after 4+ years, eat an algae sheet off a clip, but she will eat it if I break it up in the water column. The other things that is nice about breaking it up is that it will land sporatically throughout the tank, so your grazers will eat it off the rocks. I leave my return pump off for about 30 minutes. Start with small amounts to see how much you need for your fish/tank size. I have A LOT of algae eaters, so I use 1.5-2 full sheets a day in my tank and none of it is left behind.