Topping off my ponds

[Pete]

I need to top-off the water in my 100 gallon outdoor pond of White Clouds due to evaporation. In the past I've filled it 5 gal at a time, each time dechlorinating the water with a liquid dechlorinator.

Would it be harmful to just fill it with the hose and then dose it with dechlorinator? 

[Koi]

For me anything under 20% I don’t dechlorinate. But this value entirely depends on how much chlorine/chloramine in your water. 

I usually dechlorinate during filling or after when I do bigger amounts but I know my water has very little chlorine or none at all.I have started and maintained tanks without it in the past but now I use it out of fear since the risk isn’t worth the savings. The quality of municipal water can change anytime so spending a little money as insurance gives me piece of mind.

I would say put half dose at the start and the rest of the dose while filling  the water or at the end to be safe.

[Ben_RF]

If you want to take the lazy way out, you could always attach a catalytic carbon filter to your garden hose.

Here is a quick one from amazon. I personally use this one: https://www.amazon.com/Garden-Hose-Filter-Chloramines-Pesticides/dp/B007I6MN72/ref=sr_1_3?dchild=1&keywords=catalytic+carbon+filter+hose&qid=1614888891&sr=8-3

[OceanTruth]

In my opinion, I would just dose the pond with dechlorinator and fill it. I never had a problem doing it that way. I know some people are against it, but there is no one way to do things and have good results.