I’m trying to make ceviche for the first time. I’ve diced the fish, and it’s been marinating in the fridge with what looks like too much lime juice. Before I put it in there, I put in garlic powder and kosher salt. Once mixed, I sampled the juice. It’s a bit bitter. (Well, limes…) I’ve chopped up some red onion, and I have a bunch of cilantro. I’ll mix those in in about 20 minutes or so, then let it sit for another hour. I wanted to put some avocado in it, but the avocados are still a bit too firm.
It turned out well for my first attempt. A little on the tart side, but good. And one of the avocados was ripe. 
Half a teaspoon of sugar goes a long way with some acidic foods.
Yes. Don’t be afraid to add a touch of sugar. When I make pickled cucumbers, a little sugar makes all the difference in the world. Really rounds out the flavor.
Try this:
Ceviche is “on our rotation”. We have it 2-3 times a month. Tilapia, snapper, tuna, and scallops are some of the finish we like. Jalapeños always, minced habaneros occasionally. Oh, and mangoes when they are perfectly ripe.
15-20 minutes is long enough to cure ceviche. Sitting in the acid for longer times toughens meat.
Agree.