gblazzo, you are probably ok.
If anything, then your pH will change for just a very short duration, which could cause the fish to act sporatic. Most of these products contain minerals, other fish supplementals to increase their protective slime coat, and sodium thiosulfate.
Sodium thiosulfate is what neutralizes the chlorine, but the way it is made in a bottle could cause problems by causing the sodium thiosulfate to go bad due to the compound's decomposition, which
might result in the production of hydrogen sulfide (toxic to fish). The extra dechlorinator has a short shelf life in water and will be broken down by bacteria.
When in doubt, I always google the product. Often, the product will not state everything on the bottle and reading the MSDS would be a good idea as well.
gblazzo, are you positive it is chlorine and not chloramine ?? You can find out easy by using a pool test kit or calling your local water plant. Most water plants use chloramine instead of chlorine due to health concerns and due to the chloramine stays in the water longer. Sometimes the water plants will use both.
Chlorine is a gas and this gas eventually dissipates. Chloramine is created by the water plant combining the chlorine gas with ammonia so that the chlorine does not dissipate out of the water.
Chlorine can dissipate out of the water naturally by just setting it out in a container for a day (i would agitate it with a small fountain pump), very slowly trickle driping the water into the tank, or by spraying the water into the air as it is being added to the water. However, if you are doing big water changes, then it is best to add the dechlorinator
before the water change (that is after old water taken out). This method does not work for chloramines since it is bound in the water with the ammonia.
For chloramines, you have to use a dechlorinator or a chloramine carbon block filter. Keep in mind that, when the chlorine is nuetralized out of chloramine, then this releases ammonia into the water. If your bio-filter is built well, then the extra ammonia will be easily consumed by the bacteria.
I just did a quick google and found a
Chloramine carbon block filter that uses a garden hose connector. I don't know anything about it nor I do not know how often these filters have to be replaced.
Honestly, I would not use any of those dechlorinator pond products. If you want to though, SeaChem is an excellent company. Otherwise, I would just use Sodium Thiosulfate (ST) crystals and it is cheaper, but, first, if you want to use ST, then you need to know exactly your pond's gallons and know how much chlorine (or chloramine) is in your source water. Once you know this, then just add the appropriate measurement of crystals into the water. I would definitely
not make a pre-made solution out of the crystals due to the compound's decomposition possibly going bad. For the ST crystal measurement, the correct amount is 2 to 7 parts sodium thiosulfate to 1 part chlorine. Parts per million = mg/L; so, if the concentration of chlorine is 2 ppm (from your source water), then you would need 4 to 14 mg of sodium thiosulfite for every liter of water. 100 US gallons = 379 L, so for every 100 gallons, you would need 1.5 to 5.3 grams of sodium thiosulfite. Depending on the crystal size, a teaspoon is about 6 grams. It would be a good idea to get a gram scale if you want to use the ST crystals. If it is practical to do this in a seperate container, then this is best. Add the crystals before you put in the new water (that is after the old water is taken out).
