First I'm an very old timer , only 55 years with turtles. I do "not" use any man made chemicals to control the water ! Not even water conditioners ! Us old timers like to have full control of that. I/we believe in natural water cycling . Read up on it , it helps even your filter work better when it's setup for a turtle.
Here's one article on it , yes says for "fish" tank but is the same for turtles :
http://www.oscarfishlover.com/how-to-cy ... r-aquariumOne of the keys to cycling is the more water you have the easier it is to start a cycle and to maintain it.
That conditioner sounds good if statement's are true , especially with the chloramine's. From my homework Singapore has some of the cleanest / safest tap water in the world .
The bacterial one would help but watch the dates for expiration. Also how the warehouse stores it to keep the bacteria alive is a big deal....
Study up on cycling it's truly the way to go. As they grow and yes get big it will help lots ! Also save lots of money and you will have full control of the water .
One thing I would start doing is to pull up the "MSDS" (material safety data sheets) on any product you want to use to see all info on a product. Most reputable companies offer it some were on there page. If not just google it. A product named for "reptiles" are not always adequate for aquatic turtles !