I've been using API Tap Water Conditioner for years. Here's an old picture that I posted back when they changed the bottle. It's inexpensive and works great.
Ditto - I buy the 2.5L bottle - will last me a good year at least and I have more tanks than I can count. I have to use a 1ml syringe to measure out 0.5ml for a 14 litre bucket
Love it though - I was getting through a big bottle of Aquasafe a week before!
I use API Stresscoat+ at present and have done for some time now, but is a tad expensive. A friend just started using the Seachem Prime stuff and she is happy with it. I'll get a bottle of that next time and give it a go.