Commercial, scientific and residential fish owners have tanks and ponds that range from one gallon to several thousand gallons, and there is no "magic formula" for . We can give you some general ideas of what works or what others have done to neutralize chloramine:
Activated charcoal (carbon) filtration systems
Sodium thiosulfate (dechlorinates but doesn’t deal with ammonia)
Commercially available dechloramination products (check the labels, since some simply remove the chlorine, while others "lock up" or detoxify the remaining ammonia)
Catalytic ( GAC) carbon
A chemical agent plus a biological filter (agent to remove chlorine, biofilter to remove the ammonia)
It is important to test your pond water to make sure there is not a build-up of ammonia.

FACTS AND ANSWERS
Unlike chlorine, chloramine will not dissipate to the atmosphere by standing or aerating.
Boiling will not remove chloramine.
Chloramine passes through the gills of fish and directly enters their bloodstream.
In the blood, chloramine chemically binds to the iron in the hemoglobin in red blood cells causing a reduction in the cells capacity to carry oxygen.
Chemical additives for dechloraminating water you add to your tank or pond (makeup water) are available at pet/fish supply stores.
Sodium thiosulfate added to chloraminated water will neutralize chlorine, but ammonia is released.
Water should ideally be dechloraminated in a separate container to neutralize chlorine and ammonia before being added to a tank or pond.
A pond with an established biological filter (one that has cycled through the nitrogen cycle – has converted ammonia to nitrite to nitrate) can remove ammonia.
Tap water used with artificial sea salts for makeup water in salt water fish tanks must be dechloraminated.
The proper amount of neutralizing chemical is sometimes added to the pond prior to or simultaneously with the makeup water.
Water additions should be as small as possible, so the fish are not stressed as the biological filter cleanses the water. Avoid large water changes.
Adjustment of pH may be more critical because of the possible addition of ammonia. At a pH of 8.5, ammonia is about 11% un-ionized, which is the potentially toxic form but at a pH of 7.0 it is only 0.4%.
The quantity of makeup water to be added should be estimated to determine the required amount of dechloraminating chemical. The water quantity can be found using the water meter, timing the filling of a bucket, or by the amount the pond depth would increase, not the total pond volume. (Depth increase: multiply length times width times depth – all measurements in feet – to obtain the volume in cubic feet, multiply that by 7.5 to obtain the gallons of water to be added.)
Automatic makeup water systems may have to be operated manually to allow the proper amount of dechloraminating chemicals to be added simultaneously with the makeup water.
Carbon filters should be operated at a slow rate for best chloramine removal. They should be monitored carefully to determine when the carbon media has reached the end of its useful life and needs to be changed. Manufacturers often indicate the maximum number of gallons that can be filtered before renewal of the filters is required. Check with the supplier for proper operation. Testing the residual from the filter will help determine the best filtration rate.
Runoff from lawns or gardens should not be allowed to enter a pond because of the possible presence of chloramines, fertilizers, insecticides, pesticides, and/or any other material that might contaminate the pond.