Easy way to add 1 gallon of dechlorinated H20?

I am wanting to top off my aquarium with abt 1 gallon of water, but the dechlorinators are so potent I have to really cut back the doseage and am really beginning to guess at anything below 5 gallons? Is there any danger to overdosing on dechlorinator?

I have two brands of dechlorinator - Instant Ocean Marine Conditioner and Prime. Is one better than the other?

Thank you, again.
You should be using RODI water... the dechlorinators do ONLY that... take the chlorine out. There are other harmful things (to your reef) in your water that the dechlor does nothing for.
+1 Erin, but if you have to use it, just divide the dosage down. I.E.: 5ml per 10gal = 1ml per 2gal. Oh! & you really have to go out your way to overdose with any dechlorinater.
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