I use Kent's Garlic Xtreme, which is available both online and possibly at your LFS
. It's very potent garlic extract and is made specifically for aquarium use.
You can also make your own garlic juice by soaking cut up fresh garlic cloves in RO
Be wary of garlic oils or powders made for human consumption, they may contain additives that aren't good for your fish or water chemistry.
As for food, you might consider mysis shrimp or plankton instead of brine. Brine shrimp carries very little nutritional value... I've heard it compared to potato chips for fish.