Does flouridated water harm koi?

[Manky Sanke]

A question that occasionally reappears and was asked again last week is whether fluoridated water harms koi. In the absence of any research that I can find on the subject I reason the answer this way:

Pollution of the aquatic environment by sodium fluoride from some industrial processes has been linked to delayed hatching of fish eggs and reduced growth, which is why, when I clean my teeth, I rinse my mouth into the sink, not my koi pond. Apart from sodium fluoride being a compound that is a common industrial waste product, it is also an ingredient in fluoride toothpaste, but it is not added to tap water. It is a different chemical, hexa-fluoro-silicic acid, which is added to some water supplies.

Either of these two fluorides, I will happily put into my mouth, but what about isopropyl-methyl-phosphoryl fluoride? Certainly not, it is sarin gas. We must not assume that all fluorides are the same.

Fluorine gas is a highly reactive natural geological gas that forms fluoride compounds with geological solid materials that it touches. Although these compounds are only weakly soluble, ground water in contact with them will dissolve them when conditions are right. This means that natural water sources frequently contain fluorides. These natural levels are sometimes equal to, or higher than, the permitted level of artificially added fluoride. They cannot easily be removed at water treatment plants, so many of us have been drinking, and filling ponds with, naturally fluoridated water, all our lives.

As far as I am aware, there has been no scientific research into whether water that has been fluoridated with hexa-fluoro-silicic acid affects koi, so it may be helpful to consider the following and see what it tells us.

About 10% of UK water supplies have fluoride artificially added. The only practical way to remove this fluoride is by using the best quality reverse osmosis filters. Few koi keepers have these filters and I doubt that any of them fill their ponds exclusively with RO water, so it is reasonable to assume that 10% of the nation’s koi ponds contain natural or artificially fluoridated water. If this water seriously affected the koi in those ponds, then 10% of UK koi keepers would either have to abandon their hobby or go to great trouble to obtain water that does not contain fluoride.

Since this is not the case, it is my opinion that neither naturally, nor artificially, fluoridated water pose a significant threat to koi.

[Duncan]

thanks for that Syd interesting

do you know if carbon or our RO membranes take it out?

dunc

[Manky Sanke]

Can activated carbon remove fluoride? Very short answer - not reliably.

A better answer requires a little chemistry knowledge to understand it.

Chemistry 101
Atoms can be likened to little solar systems where electrons obit a central nucleus similar to the way planets orbit the sun. The nucleus is made of protons and neutrons. There is always the same number of protons in the nucleus as there are electrons orbiting it but there can be variations in the number of neutrons. These variations are called isotopes and the picture below shows three isotopes of carbon - carbon 12, carbon 13 and carbon 14. they all have 6 protons and 6 electrons but there are 6, 7 or 8 neutrons.
Class dismissed





With that in mind, the proper answer is that there is some evidence to say that very slow flow rates through activated carbon will reduce the level of fluoride but this appears to be a complete elimination of one or more of the isotopes rather than a reduction in any fluorine isotope that passes through it. So it depends on which isotope is passing through a filter as to whether it will remove all of it or none of it.



Can reverse osmosis filters remove fluorides? Very short answer - not reliably.

A better answer only requires a little understanding. Fluorine is a small atom that is highly reactive and so will form compounds called fluorides with many substances it touches. The size of the resulting fluoride molecule depends more on the molecular size of the substance that reacted with the fluorine than the original size of the fluorine atom.

Reverse osmosis filters can be thought of as sieves - big things are stopped, little things go straight through. So, as I said in my post:
"The only practical way to remove this fluoride is by using the best quality reverse osmosis filters. Few koi keepers have these filters..."
If you have a very good quality, (and therefore very expensive), reverse osmosis membrane it will stop all fluorides. Cheaper membranes will stop some of the larger fluorides but not necessarily the smaller ones.

I would hazard a guess that most reverse osmosis filters, if not all of them, will remove the fluoride added by water treatment plants (hexa-fluoro-silicic acid) but some of the naturally occurring fluorides that can be in the supply water can have smaller molecules and might get through.


Anyone who finds the full answers hard to understand should remember the short answers - not reliably.

[Duncan]

kinda like oxygen isotopes. so I guess going back to your original post we should just ignore it

dunc

[Manky Sanke]

I can't quote any reference or research that proves that natural or artificially fluoridated water has no noticeable effect on koi but, from the reasoning above, Ignoring fluoride was my conclusion. I can't see any flaw in the argument but I'd welcome it if anyone has any comments or pointers to any research on the subject.