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Have read up on the issue and contacted the Norwegian water authorities for a comment. When water evaporates it is basically distilled and completely clean. The contamination process happens as the rain falls through the sky on the way down, coming in contact with potential contaminants. Mostly these are acidic molecules that cause acid rain and some particulate matter (PM). In very specific and polluted areas other molecules such as PFAS (flame retardants) may also become part of the rain drop.

  • The rain where I live is not contaminated with either acidic molecules or environmental contaminants. Even in case of long-range transport of ash or sand, not enough to make the rain acutely toxic for organisms. The rain that fall here consistently has a PH of 5.5 which is the same as your OR water after it has been in contact with air.
  • As someone correctly pointed out the rain may be clean, but the rainwater that ends up in your reservoir is not. This is where the pollution happens. So unless you are absolutely sure that your collection method is clean you might end up with a contaminated terrarium. (Collecting fresh snow would eliminate this problem, but that is not for everyone).
  • Since one has only bioaccumulation in the terrarium, not biomagnification it is extremely unlikely that concentrations of contaminants will build up sufficiently to harm living organisms if your rain and collection method is clean.

All in all, after some consideration, I would be extremely restrictive in the use of collected rainwater.

But, I would also be very concerned with using only RO water without making sure that the frogs had access to/were replenished with minerals and trace elements that are necessarily washed out through their permeable skin. In addition, RO water that has not been in contact with air contains no oxygen and has a PH much higher than the frogs would be exposed to in nature (although the replenishing process happens rather quickly).
 

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The rain that fall here consistently has a PH of 5.5 which is the same as your OR water after it has been in contact with air.
The water that comes out of the osmosis machine is pH neutral and therefore has a pH value of 7.

The frog's skin is thin, moist and contains many blood vessels. Frogs drink and breathe through the skin. They do not swallow water, they get all the water they need through their skin and by eating food animals.
 

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Reverse osmosis water is nearly pure water with a PH of 7.
Agreed, but it only needs a reatively short exposure time to air to become 5.5 again. 10 minutes in ideal conditions, but much more in a tank of course.
 

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but it only needs a reatively short exposure time to air to become 5.5 again. 10 minutes in ideal conditions, but much more in a tank of course.
The PH value will indeed change when it comes into contact with another substance such as the substrate.

But back to the advice in this topic: RO water is used because it is clean, so it will not transfer diseases and contaminants quickly. And as a plus, no limescale deposits on plant leaves, which by the way will not bother you with rainwater.
 

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I believe we are in agreement, but there is also the element of being too clean and sterile.

Before I used RO water I would make sure to bring it back to the PH and oxygen characteristics of rainwater. This would easily be accomplished with a small circulation pump un the RO reservoir while exposed to air.

And one more question. Neither the RO water nor the plant-based substrate in a terrarium will release sufficient salts, minerals or trace elements. I also seem to remember that these resources are very scarce in the rainforests. Is it believed that the frogs acquire all needed substances through food?
 

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And one more question. Neither the RO water nor the plant-based substrate in a terrarium will release sufficient salts, minerals or trace elements. I also seem to remember that these resources are very scarce in the rainforests. Is it believed that the frogs acquire all needed substances through food?
I don't really dare to make a statement about this. But I think the necessary substances come from the food and preparation additives.
 

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The pH of RO water is irrelevant. It varies from 7 down depending on CO2 concentration, which affects neither the frogs nor the plants in the situations in which we use it (atmospheric CO2). It is simply a non-issue. The pH of rainwater is driven in part by SO2 and nitrogen oxides, which are issues.

The pH of very pure (i.e. RO) water is a theoretical determination (it is 7), in part since pH probes don't behave reliably in pure water because there are no ions to measure (the pH of water is a mathematical relationship between free H+ and OH- ions). Not that the concentration of oxygen is relevant (and it does not affect pH) relevant, but RO water contains plenty of oxygen, since RO processing does not remove dissolved gases, and pressurized source water is typically supersaturated with dissolved atmospheric gases. All this can be easily confirmed by a simple web search.

RO water and ABG and frog poop has been shown by thousands of keepers over decades to reliably grow many species of plants really, really well.

Frogs can move ions through their drinking patch (and, likely, ions move through their skin constantly, which is one reason why the purity of the water that is forced on them in captivity is so important), which is one reason some keepers are seeing benefits from various applications of clay and similar substrates. Given the frequency with which we see threads here regarding build up of supplement dust in vivs, dart frog vivs substrate likely becomes high in salts, etc. fairly quickly.

As to the 'minerals washed out through skin' claim (which I take to refer to passive ion loss, which active ion transport mechanisms counter), to prevent this by applying only isotonic (i.e. haing the same mineral content as frog blood plasma) liquids to the viv would be disastrous. The osmotic pressure difference relative to frog plasma of RO water and rain water is nearly the same and would make no little physiological difference.
 

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Did you guys read the early posts in this thread? They address concerns about RO and distilled being bad for frog husbandry. RO water doesn't have magic properties that make it permanently a certain way. As @Robru said, the water is interacting with its environment as soon as it goes into the tank. Gas concentrations are dynamic and the water will quickly move to an equilibrium for all gasses and mineral content once introduced to the tank. The water doesn't stay sterile permanently - it is quickly modified by its environment, especially when it is being introduced in very small droplets (mist from our misters). I think that RO water would be pretty similar to other kinds of water (rain? tap?) in the tank after a fairly short time period.

Mark
 

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Thank you for the information in the process only removing CO2, not O2, that is informative.

PH7 may be an non-issue, but natural clean rain that frogs are exposed to in nature has a PH of 5.5 which is 32 times more acidic that than PH neutral RO water. I think the question may be warranted at least. (Or in light of the new post, if this happens rather instantly through misting, then maybe not.)

I will look up more info on adding clay.
 

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Thank you for the information in the process only removing CO2, not O2, that is informative.
Apparently I wasn't clear. RO membranes do not remove any dissolved gases, neither CO2 nor O2 (nor N2, nor Rn, nor Cl, etc). Other, sometimes associated, methods do remove some of these (e.g. activated carbon can remove Cl) but I don't know of any practical way to get dissolved CO2 or O2 below atmospheric concentrations (degassing with air preprocessed by a sodium hydroxide based CO2 scrubber would be one way, though very cumbersome and materials-intensive).

Again, none of that is relevant to dart keeping. I'd highly recommend that novice keepers at least try the established practices that have been worked out over many years by many keepers. Very few reinventions of the wheel have positive outcomes, especially when pursued without much understanding of the need for doing so. I apologize if that comes off as harsh, but many of the concerns that have been raised here are based in simple factual error, and many of the rest can be shown by experience to be irrelevant. I'm not sure how to say this more respectfully; if I could, I would.
 

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You were clear, but I got confused when reading this earlier: https://www.123filter.com/ac/why-reverse-osmosis-water-is-acidic

No worries, I was convinced that my natural rain collection method was ideal, but see that I was wrong. That being said, I hope there will be some new wheel-reinventions down the road in some aspects of frog keeping, it would be boring to have all the answers :)
 

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I look forward to this too, @Anda! If you look back at the last decade or so in keeping, there have been some really important changes to the hobby with huge implications to the health of our animals. A few that come to mind are 1) better supplementation that has almost eliminated problems like spindly leg syndrome 2) LED lighting that has made it much safer for the frogs to avoid heat exposure and 3) better understanding of ventilation and humidity in our tanks (though some of this progress has been eroded by trends in social media influencers showing tank designs that don't reflect best husbandry practices). I am absolutely certain there are lots of things left to be discovered in dart frog keeping!

Mark
 

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No worries, I was convinced that my natural rain collection method was ideal, but see that I was wrong. That being said, I hope there will be some new wheel-reinventions down the road in some aspects of frog keeping, it would be boring to have all the answer
You are right about that. Let's keep looking ahead and get more and more knowledge, then we will be better able to keep frogs and other animals indoors (y)
 

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I have read the many posts that have popped up since I first posted with great interest. My conclusion would be that in some cases rain water may be totally fine, especially if it is collected in a clean receptacle, and even more so if it subsequently filtered.
Where I live on Vancouver Island, we receive 4+ meters of rain per year. There is minimal industry / airborne pollution around here. While I readily recognize that some airborne pollutants can indeed travel thousands of kilometers, it seems unlikely that they could possible naturally concentrate in any harmful levels. Assuming the rain water is further filtered through activated charcoal (for example), whatever trace amounts of harmful chemicals or toxins remain would seem extremely unlikely to pose any threat. The abundance and diversity of indigenous amphibain species that thrive here would suggest as much.
The point about bioaccumulation is factually incorrect. Dissolved substances could accumulate in a system in which water was continually added and allowed to evaporate (how hard water stains form in a kettle), but in a vivarium the water is constantly replaced. The vast majority percolates through the substrate and is drained out, the rest is transpired by the plants / frogs, and in neither case would anything accumulate.
I do not disagree with the notion that RO water is pure and safe and offers a certain peace of mind, but I do find it hard to believe that even an amphibian could be so susceptible to microdoses of contaminants in rain water that you could see adverse effects in a vivarium environment.
I would be very interested to learn more about the possible role of airborne pollutants in amphibian declines. The majority of research on water-borne pollutants seems to focus on substances introduced or leached into the water table rather than released into the air.
 
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