First, I don't really suggest RO or RO/DI water for any tank other than saltwater tanks. RO/DI water is stripped of it's buffering capacity and can cause pH swings. It's fine for topping off a tank that was originally filled with tap water (if the tap water had sufficient buffer to begin with) because the dissolved minerals won't evaporate although some may deposit as solids on the glass & equipment.
Once a tank is up and running (cycled) I would just use tap water to top off. Don't worry about buffers or minerals becoming concentrated in your tank due to evaporation because you'll be removing part of the water and replacing it with new during scheduled water changes anyway.
If you -are- going to be using RO water in a freshwater tank you should be using a product like "RO Right" or some other buffer to prevent pH swings and restore the necessary mineral content to the water.
As for whether to add prime now or not.. After a week's time it really wouldn't matter. If your municipality is using chlorine it's certainly all outgassed by now. If your municipality is using chloramine then I'm sure most if not all would also be outgassed in a weeks time if you have a filter running in the tank (water agitation).
Many aquarium keepers don't use a dechlorinator such as prime, amquel, stress coat, etc at all; some age water so that chlorine / chloramine is outgassed naturally. The problem with chloramine though is that even once the chlorine/amine bond is broken and the chlorine outgassed it leaves behind ammonia compounds. Call your water board / water authority and ask which they use. If it's chloramine then you should keep on top of using a dechlor product even if aging water before use in your tank as the better dechlorinators out there (like prime) help detoxify the remaining ammonia.
Just my $0.02
Ric
Once a tank is up and running (cycled) I would just use tap water to top off. Don't worry about buffers or minerals becoming concentrated in your tank due to evaporation because you'll be removing part of the water and replacing it with new during scheduled water changes anyway.
If you -are- going to be using RO water in a freshwater tank you should be using a product like "RO Right" or some other buffer to prevent pH swings and restore the necessary mineral content to the water.
As for whether to add prime now or not.. After a week's time it really wouldn't matter. If your municipality is using chlorine it's certainly all outgassed by now. If your municipality is using chloramine then I'm sure most if not all would also be outgassed in a weeks time if you have a filter running in the tank (water agitation).
Many aquarium keepers don't use a dechlorinator such as prime, amquel, stress coat, etc at all; some age water so that chlorine / chloramine is outgassed naturally. The problem with chloramine though is that even once the chlorine/amine bond is broken and the chlorine outgassed it leaves behind ammonia compounds. Call your water board / water authority and ask which they use. If it's chloramine then you should keep on top of using a dechlor product even if aging water before use in your tank as the better dechlorinators out there (like prime) help detoxify the remaining ammonia.
Just my $0.02
Ric
