Wow! Lots of great information here. I have questions to get more details from everyone.

First, I have always done the method of letting tap water sit out for a day or 2 before using it. I have never seen ill effects on adult or juvenile frogs. I had a breeding group of Clown Tree Frogs for quite a while and the few times I got tadpoles I can say that they never survived a water change with my "aged" water. I have raised Red Eye Tree Frog tadpoles with the aged water and had great success. And yes the water spots are always terrible!

Secondly, I have moved to 3 different cities in the past 4 years and have noticed extreme differences in the tap water. I own a group of aquatic Caecilians and noticed that when I lived in an area with hard water they did terrible. Their skin seemed to get more plastic looking than soft and rubbery like normal. (This is something to look out for depending on your water supply) After noticing the change in health I purchased a R/O unit sold in aquarium shops(maybe Coralife) and this made the difference. I've never experimented with adding minerals back into the water though.

For those who do a lot with dart frogs, what is the ideal pH you've used to maintain and breed with?

As far as using products like R/O Right, do you have any recommendations for the proper mixture?

Reverse osmosis water conditioner for freshwater aquariums*Contains a special mixture of dissolvable solids to condition RO water*Provides desirable trace minerals necessary for healthy aquarium inhabitants

A perfect mix of salts and trace elements to balance RO and deionized water, including calcium, sodium, potassium, and magnesium. Phosphate- and nitrate-free. Use for both soft and hard water. Powder: For soft water - 1/2 teaspoon per 10 gallons of water. Medium hardness - 2 teaspoons per 10 gallons. Hard water - 3 teaspoons per 10 gallons.
Liquid: 1-5 teaspoons per 5 gallons; depending on the hardness of water.

Here is guidelines I've found for R/O Right, but as far as frogs go, I'm at a loss to decide which way to dose the water.

As for the Holtfreter's Solution, do you use this at 100%?
This is the only formula I've seen listed as 100% Is this correct?
NaCl3.5 gNaHCO30.2 gKCl0.05 gMgSO4 stock solution333 µlCaCl2 stock solution333 µldH201 liter
Check pH; should be between 7 and 7.5.

I know there is probably something else I want to add to this but it is now tomorrow morning and I need to get some sleep before work.