I can't answer the first question, but as far as dosing the entire tank before adding water, it you use the bucket method, you can just add a few drops of dechlor per bucket while filling the tank.

 

If you are referring to Seachem Prime water conditioner, their FAQ section states that it will bind to ammonia for 24-48 hours after dosing. Ideally though you should know how much chlorine or ammonia is in your tap water for the best Prime dosing results so you don't overdose or underdose the product.

As to your question regarding dosing new water to the tank for Prime, you only need to dose for the entire tank volume IF you are adding water directly to the tank via a hose. If you are using a bucket or container to add new water, just dose per the instructions for that amount of water as @ustabefast suggested.

Usually I just treat new water going into the tank but it I started testing out just filling up the whole tank from the house especially for the outdoor tanks.

I am digging a pond so I may be required unable to just treat new water in that situation. It might be easier to figure out the pond size in terms of gallons and just add when its time for a water change.

I was just wondering why treat the entire volume instead of just for the amount of chlorine being introduced into the tank/pond. There must be a reason or else they would not advise to do this.

 

If you are referring to Seachem Prime water conditioner, their FAQ section states that it will bind to ammonia for 24-48 hours after dosing. Ideally though you should know how much chlorine or ammonia is in your tap water for the best Prime dosing results so you don't overdose or underdose the product.

As to your question regarding dosing new water to the tank for Prime, you only need to dose for the entire tank volume IF you are adding water directly to the tank via a hose. If you are using a bucket or container to add new water, just dose per the instructions for that amount of water as @ustabefast suggested.

 

Ideally though you should know how much chlorine or ammonia is in your tap water for the best Prime dosing results so you don't overdose or underdose the product.

I'm curious about this. Is there actually some kind of guidance for this other than "For exceptionally high chloramine concentrations, a double dose may be used safely. "

 

Thanks, that makes a lot of sense. I've skimmed the first part of the article but will definitely be working my way through the rest of it.