I don't use the liquid but I've been using the shock crystals for over a year now and it works great.
Mix 1 tsp of shock crystals with 1 gallon of water. This will Give you a weak solution. Now you add this solution to your res, I put it in my veg flower and cloner. You want to add the solution at 1 oz per gallon of water in the res. Because the chlorine does evaporate out over time it's good to add solution Every 3-4 days.
I have been growing hydro for 5 years now. I've only actually had res issues about twice in that time but obviously always want to prevent any future problems. I've used h2o2 it worked ok, but the shock solution is drastically cheaper and is sooo easy.
I used to let my water sit to evaporate the chlorine from the city water. Then I started learning about plants actually needing some chlorine for growth. I started using chlorinated tap water on my clones first. When they thrived I decided to try the shock in my res. so far I'm completely happy.