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I'll second that one. The LD50 for many plants and fish are well below North American and European max chlorine/chloramine levels for tap. Use your water conditioner, aeration, overnight stands etc. depending on which one you've got.

-Philosophos
 

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The issue here is a hard one to nail down. The LD50 with fish is far lower than plants; this tends to be the chronic issue. For plant keepers, shrimp become a further concern. Pinning down plants becomes a species-specific issue very rapidly (check out iron consumption and the rate carbon is sucked up through the roots vs. as CO2). On top of that, chlorine, much as copper, becomes an issue of chronic toxicity for plants, much as Cu or Pb toxicity in humans can be chronic.

In short, i'd say that a little chlorine now and then won't hurt plants so much as fish. Plants will take longer to respond, and the issue of chloramine vs. chlorine comes in as well.

Speaking purely from my experience with chlorinated tap water, you can get away with a little now and then when it comes to plants. I used to do the odd chlorinated 5-10% top-off with things like blue rams when I was new to the hobby. I'm not sure the fish were eager, but they didn't visibly suffer. At the same time, the algae dissipated at a greater rate after the top-off than they did after a 20-30% water change. While it may not have zeroed out the growth for algae, it was retardant enough to allow my simple bacopas, anubias and java fern to better compete.

-Philosophos
 

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It's the dose that makes the poison. Excel is essentially glutaraldehyde when you get around the trade names. It's cidex sold at 4x the cost or more. It's biocidal, effective enough at 100% concentration to turn your skin in to goo. At the right concentration, it kills algae and bacteria, and increases the hatch rate of some fish and inverts.

I think what we need here is some good research. All I've got is toxicity for some weeds few people keep, under conditions nobody keeps their fish tanks in. They serve as a pointless early warning, given that fish are even more sensitive. I could put them forth as relevant and absolute, but I've seen enough bad comparisons of this sort passed off, even from otherwise reputable sources. Stuff like this comes to mind.

-Philosophos
 

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Hi, I've been making my water change whit 100% tap water directly form de tap to the aquarium, this didn't seem to bother neither the plants or the fish...

Also both of them seems to like this, since the water is colder than the one in the aquarium seem to appear that the difference are good for them since the fhis star to courtship and the plants begin to bubble...

Regards
The cold, fresh water is simulating spring run-off from melting snow and/or the rainy season, and will encourage many different kinds of fish to spawn. The high agitation from dumping the water in will add air, which means both CO2 and O2 increase in a non-CO2 tank. In a tank running CO2, there's a comparative loss of CO2 but a gain of O2. From there, the heavy saturation causes the O2 provided by the plants to bubble and float to the surface, rather than dissolving.

None of these things are directly related to chlorine or chloramine, and neither negate the effects they typically have on fish or plants.

With chlorine, sometimes a vigorous pour from the tap and dump in to the tank gasses off a large part of it, which for you may be enough to avoid negative side effects. While not exactly good science, I've observed the effect my self by drinking water poured gently from a tap, compared to water poured rapidly and shaken well. The agitated one tasted far less of chlorine.

In the case of chloramine, which I'm guessing you probably don't have in your supply, nothing gasses off. The chemical stays in the water until it is chemically removed. Chloramine has a far worse reputation in the hobby.

-Philosophos
 

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Ya, .25 is low compared to the .4ppm US EPA max. I can't remember what the regulations are back home in Canada, and I imagine there are worse creatures in the tap water to fear from Mexico. If I only had to deal with .25 ppm chlorine, I'd probably be happy with an agressive pour in to a bucket, and leaving the water stand overnight if I didn't want to dechlor.

I tend to be a purist with my water; I'm soon flipping to tap for the first time rather than pure RO with custom nutrients, and I'll actually be bothering the water company for their yearly min/max/avg levels of everything they test for.

I like to think of tap water as the biggest uncontrolled variable in the tank, with the biggest impact. Entire fert dosing regimens can change based on 1ppm PO4 coming from a new farm in the right place, or Cu leaching in from old rusty pipes.

-Philosophos
 

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Oops, that' should've read 4ppm. And yes, double pouring will help a lot. I'm not sure how low it would gas off to then. This might be a topic worth looking in to further, maybe with some test kits to see just how much chlorine is left after double pouring various controlled levels of chlorine.

-Philosophos
 
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