R/O water and mineral deficiency

[JuiceBox52]

This is something I’ve been meaning to post for quite awhile. I know that some big fish keepers (Ian Fuller for one) have kept certain species from extremely soft water sources in full reverse osmosis water, without remineralizing it or mixing with non R/O water.

I know for humans, reverse osmosis can actually strip us of our bodily minerals and cause mineral deficiency.
I would assume it would do the same in fish, so wouldn’t it be absolutely vital to remineralize it? Despite them coming from a 0GH water, there’s a difference between natural 0GH and 0GH “dead” R/O water.

Just my take, I know some people keep certain species in straight R/O
Article 1
Article 2

@Byron , this might be something you would be interested in

 

[WhistlingBadger]

Depends on the fish, I think. Many of the blackwater species of Malaysia and Indonesia require water so low in mineral content that the water will barely even conduct electricity. I suspect these fish get the minerals they need from their food rather than from the water itself. These fish would seem to do well in R/O water with tannins added. I'd say these specialists are the exception though. Most softwater fish do not benefit from water that soft.

 

[WhistlingBadger]

Many of the blackwater species of Malaysia and Indonesia require water so low in mineral content that the water will barely even conduct electricity.

(this low-conductivity water might have an added health benefit if you ever drop your light fixture into the tank)

 

[Byron]

Glad to comment on this. And the direct answer is, no, fish and humans are not the same when it comes to RO water. I did not read the linked articles after I saw they were dealing with human issues, so here I am commenting on freshwater fish. As I hope I will bee able to explain, fish have very different physiologies.

Unlike marine fish, each species of freshwater fish has evolved over thousands of years to function in a very specific environment. The fish's physiology functions according to how it has evolved, suited to the very limiting environment factors of each species. Their physiology is completely different from terrestrial animals, and dependent upon the water in which they have evolved to live. This includes any calcium dissolved in the water, because calcium is able to diffuse across the cell membranes so it enters the fish's bloodstream in the water the fish is continually assimilating via osmosis. The kidneys filter this calcium out, but when it is significant the calcium blocks the kidneys, and the fish dies. A study in Germany reported in TFH found that the demise of cardinal tetras was tied to the level of the GH; the higher the GH, the shorter the fish's lifespan. Upon necropsy, it was found that death had occurred from calcium blockage in the kidney tubes.

Fish from very soft waters where the GH is zero up to maybe 1 dH are able to obtain the necessary nutrients from the food they eat. However, each fish species has varying needs for this. So we have fish evolved in harder water which have a need for minerals in the water, that is how they are designed as a product of their evolution. This goes well beyond just food of course; these fishes physiology simply cannot function well in soft water.

I had aquaria for some 30 years, living here in an area of very soft water. The water authority used to say the GH was 7 ppm, which is less than half of one degree, very, very soft indeed. I kept fish suited to such water, and I never had any issues that could be related to the GH. My fish were spawning all the time, though most eggs got eaten in my fish-full tanks, but I never added any mineral to the water except for one tank of mollies, and one of rift lake cichlids, back in the 1980's. Too much fuss and bother, when there were innumerable species of very soft water fish eager to thrive in my tanks.

 

[10 Tanks]

This is something I’ve been meaning to post for quite awhile. I know that some big fish keepers (Ian Fuller for one) have kept certain species from extremely soft water sources in full reverse osmosis water, without remineralizing it or mixing with non R/O water.

I know for humans, reverse osmosis can actually strip us of our bodily minerals and cause mineral deficiency.
I would assume it would do the same in fish, so wouldn’t it be absolutely vital to remineralize it? Despite them coming from a 0GH water, there’s a difference between natural 0GH and 0GH “dead” R/O water.

Just my take, I know some people keep certain species in straight R/O
Article 1
Article 2

@Byron , this might be something you would be interested in

Hello Juice. Good topic. I've used this type of water in tanks that require no water changes. Still fully stocked with fish, but you use Chinese Evergreen plants to filter out all the forms of nitrogen from the water in the tank. The fish waste material replaces all the minerals in the water that's absent in the R/O or distilled water.

10 Tanks

 

[seangee]

To the original articles, I read a lot on this when I started using RO for my fish and decided that my local tap water is not fit for human consumption (my decision; it tests within the legal limits for everything).

Water is not our primary source of minerals. As long as you eat a healthy, balanced diet you will get everything you need and drinking pure water will not strip this out. For people who are malnourished fresh clean water is preferable to RO water as they are not getting these minerals anywhere else, but in the case of malnourishment due to poverty clean fresh water may not be available (and neither will RO). In the case of malnourishment because of choice of diet there is a far bigger problem than the water you drink. There may be cause for concern if you were to drink 20 litres a day but assuming an average of 2 litres a day you will do no harm. And I will continue using it for drinking, cooking as well as tea, coffee etc. (and of course my soft water fish)

 

[StevenF]

I use RO water in my tank. There are a couple ofthings you need to keep in mine. RO filters are not 100% effective and as a result the RO water may have a small amount of minerals left in it. The effectivnesss of RO filters is dependent on the source water.

The other issue is that feeding fish adds minerals to the water So if you have enough fish and feed them enough the fish can remineralis the water enough to make the water comfortable to the fish.

I know for humans, reverse osmosis can actually strip us of our bodily minerals and cause mineral deficiency.
I would assume it would do the same in fish, so wouldn’t it be absolutely vital to remineralize it?

RO water doesn't strip minerals trom the body in any meaningfull amount. For the most part it simply moves things around. The death in your mouth have evolved to be mostly immune to water erosion. but the saliva in your mouth has minerals as well as any small pieces of food in your mouth. so when you drinkRO water or rain water the water will flush it into the digestive system were most of the minerals and water are re absorbed into the body. The body mainly dumps excess minerals you don't need. For the most part99% of the minerals you need come from food not the water you drink.

There are small communities throughout the world that get 99% of their water from rain falling on hard granite which is mostly silicon dioxide. so the water is basically as good or better than RO water. And as long as they have a healthy diet they are fine.

The termim remineralization in this hobby refers to adding calcium and magnesium to the water. All animals and plants need calcium and magnesium. but animals also need other elements and most of those come from food not the water. fish are mostly the same they get most of what they need through the food they eat but since they live in water they can extract some elements from the water.

 

[Traumfahrer]

I would assume it would do the same in fish, so wouldn’t it be absolutely vital to remineralize it? Despite them coming from a 0GH water, there’s a difference between natural 0GH and 0GH “dead” R/O water.

Not for some species that adapted to such water. Some of the blackwater species of Indonesia (Borneo esp.), Malaysia and tropical SE Asia evolved to live in absolutely mineral deprived water. I've read that the TDS might be as low as 18ppm.

Those aquatic encironments are characterized by the presence of a lot of tannins and humic acids especially. So it is right that you shouldn't just use Distilled Water. R/O water though usually also has some minerals left unlike truly pure distilled water.

In any case, such environments can not be established over night (as an aquarium setup I mean) and fishes have to be slowly and carefully acclimatized to that. Osmotic stress and shock, often resulting in disease and death is definitely a thing. Chili Rasboras are unfortunately often just dropped into such low hardness setups and often die within a couple of days, eventhough they'd be very fine with these parameters if acclimatized carefully.