Well a few thoughts, not all related to the original question mind you.
I do think your substrate is going to need changed out. A pain yes, but a pain that is better off being handled now than in the future when it is a bigger issue. You didn't provide much in the way of specs so I'm stabbing in the dark on a few things.
- Do you have a sump or fuge? Mostly asking because some macroalgae to help export the nitrates would help.
- You mentioned that you had just done a 25% water change. What is your water change schedule?
- I agree with Niko about getting a new source of water and I'd have the store test their water for you while you're there.
- I also agree with Niko about the tank being too small for the tang. Mine is in a 55 and I'm keeping an eye peeled for when he needs a bigger home if that day should come. I can't imagine him being in a 29. On the food, I don't see any herbivore foods for the tang listed. It is vital that he eats primarily greens. My tang is definitely an omnivore the way he chows down on carnivore foods but he is fat and happy because of his marine greens.
- Where are you getting the live brine shrimp? From a LFS? Are you adding the water they come in to your tank? Are you trying to buy a bunch and then spreading out portions throughout the week? Either of these could be problematic for your tank.
- Overall I'd look at changing your feeding a bit. A better variety of healthier fare for what each of your specimens need.
- Sometimes false percs never host. Some feel it is bred out of them, who knows. It is always a gamble.
