i have been searching the net for an answer for you but they are hard to find. i found this. but it would be hard to do with 4000 gallons.

City Water & Chlorine

City water treatment plants vary the amount of chlorine and/or chloramines depending on the time of year and amount of rain. The very best way to add water is to first put the water into a separate container add your de-chlorinator and then test for chlorine. Use a good de-chlorinator such as Amquel, Aqua Safe, or, if you have a large pond, Sodium Thiosulfate is available from Aquaculture supply houses. De-chlorinators should be added to the water before any fresh water is introduced. Chloramines are a combination of Chlorine and Ammonia. When you add your standard de-chlorinator, the Chlorine is eliminated, but the Ammonia stays in the water until your bio filter converts it to more harmless Nitrates. Only products that specifically mention Ammonia binding such as Amquel (tm) will bind the Ammonia in a harmless state, until your bio filter bugs can convert it.

Did you know that even small amounts of Chlorine can eat away at your fish's gills, weakening and stressing them?

maybe it would be possible for you to take your fish out while you add the watter and declorinator? if not i would sugest maybe putting in a little bit of declorinator as you add the water.

Laura,
Thanks for the article.
I did go ahead and add the dechlor first.

you are so welcome hun, did things go well putting in the declor fist?? i searched and searched for an answer but there was nothing that i could find that really adressed it directly.

i'm lucky in a way . i have well water, it is very soft water so i have to use ph buffer and stablizer. i also use koi clay weekly. but it works ...

have a wonderful night laura

Hi 1sst. I use my settling chamber for water changes so can fill it (300 gals) then add the dechlor and start the pump on that line. Before I had a settling chamber I dosed the pond first then added new water. Most of the stuff says it works instantly although I seem to remember some discussion about that here. I never had a problem when I added treatment first then water.

Did you get your air pump???

I decided to err on the side of caution and I added the dechlor first and last.LOL
It took 7 hours to fill the pond and I wanted to make sure the dechlor was still working.
Jalal, I finally found an air pump locally. I still am tweaking it just to get it right.

I had a similiar situation awhile back and through this forum I chose to buy Systems IV garden hose Chlorine/Chloramine filter. Seems to work well but I haven't tested the water after doing a partial water change, fish seemed very happy. The filter is advertised to filter 7500-10,000 gal. of city type water. I paid $34. from PondBiz. As I am gone alot it makes it easier for my Wife to just screw filter on hose, partially open valve and set timer than to measure/mix dechlorinator. FYI for gardenters; I've used pond water as a base for making aerobic compost tea and the plants have really thrived.

When I have had to add more then a thousand gallons I have added dechlor, filled for awhile, added more dechlor...ect. So far the Koi have lived over 11 years with this method so I think it is solid. I try to stretch out the big water changes over as many hours as I can due to the difference in temperature of the tap water vs pond water. Just something to consider.

Lisa

Since chlorine will burn a fish's gills,as will chloramines, so it is best to add a small amount of dechlor, into the pond first when doing major water changes.
This will protect the fish from the start of the fill up with new water.
Read the instructions as to dosage and add some dechlor, to what water is in the pond, before you do the filling. Add some again as you go and some at the end.
As long as you have a reasonable idea of what gallonage of water you are treating and you just don't pour in the whole bottle of dechlor, it would be difficult to over-treat.
"Horton"

I decided to add it in the beginning and towards the end of filling it in order to cover all my bases.

Thanks!

Horton,

I've only used AquaSafe Dechlor. so I'm not too familiar with other brands but I thought it was next to impossible to add too much and "over-treat" a pond?

Can you enlighten me?

I've always preferred to error on the side of caution and "over-treat" my pond... I add as I go along, about every ten gallons.

pondbucket, My statement was purely cautionary.

My intention in making that statement was, if a person goes by the recommended dosage for the amount of water being treated, it would be, as I stated, in the other post, difficult to over-treat. I will now add,..... and possibly cause a problem.

I would think when adding any treatment to your pond, for whatever reason, it would be advisable to stay with the dosage recommended by the product manufacturer.

I don't know for sure, if you could in fact overdose with any pond dechlorinating product, but if the manufacturer states that, "X" number of ounces of this product,treats so many gallons of water, that is what I'd go by just to be safe.

I would not like any one to get the idea that doubling up on any treatment dosage, would do double the good, in half the time.
To me that could be a dangerous conception.

"Horton"

Okay, I see... and I agree... though I think I've read one dechlor product (and I'm not sure it's Aqua Safe) that you could not over dose.

Still, thanks for the clarification.

I'll see if I can find the product literature, and if I do I'll post.

It is possible to overdose with certain dechlorinating agents. Sodium thiosulfate is one agent that is used in some formulations. This material will also react with dissolved oxygen. Therefore if you used large amounts of this material you could potentially create a depleted or significantly reduced oxygen level. It will react with chlorine first, however.
---David