Fluoride.

[Vale!]

Sorry – I’d been waiting for a couple of replies to emails (non-delivered because the recipients have since moved on from their respective institutions) and a ‘within 48hrs’ reply from my Water Authority. The latter arrived yesterday, just to confirm that the average fluoride concentration here during the first half of this year, 0.271mg/l, referred to the fluoride ion (F^-). The legal limit in the UK is 1.5mg/l. In the interim I eventually found reference implying the same in some of the literature I’d come across. Some notes from that …

The F^- ion is aggressively reactive and tends to want to replace less reactive ions, such as that of calcium, in tissues.

Fluoride in water is widely researched - particularly, it seems, in India where there are ‘pockets’ of relatively high fluoride concentrations in groundwater which enters the food chain via consumption of fish. Low levels don't cause life-threatening issues to humans but the “gradual bioaccumulation causes toxic effects in living organisms and consequences can be fatal. Fluoride intoxication in fishes needs to be controlled in order to prevent ill health in humans”.

Where drinking water is concerned, it’s reckoned that concentrations of less than 0.5mg/l or greater than 1.5mg/l can negatively affect bone and teeth structure in humans. Again in humans, 93% of ingested fluoride is absorbed into the bloodstream. A proportion of this is excreted but the remainder stays (and builds up) and can cause the condition ‘fluorosis’.


The same can happen in fish but studies that I came across were based on very high concentrations of fluoride. A typical ‘for instance’: carp were variously exposed to 35mg/l to 124mg/l of fluoride and sampled at 30, 60 and 90 days. They found that fluoride concentration in tissues increased with level and duration of exposure – it accumulates rather than is metabolised away. Gills accumulated the highest level of fluoride, then liver, brain, kidney, muscle and intestine in that order. Such (impossibly in nature?) high concentrations promoted ‘oxidative stress’ in the fish (I think that means the creation of free radicals) and could lead to chronic toxicity.

In other studies multiple other effects were noted: delays in hatching time (at 1.5mg/l) ; growth inhibition ; damage to eggs and sperm ; and chromatophores (pigment cells in skin) changing shape and distribution.

An interesting (to me) note was that in soft water, fluoride concentration of 0.5mg/l can cause toxic effects in invertebrates and fish living in fresh water due to low ionic concentration (I didn’t fully understand this). And, incidentally, plants have been reported to accumulate fluoride (although I didn’t follow that one up).

So as fishkeepers the general takeaway seems to be that the levels of fluoride in our typical tapwater should not cause us undue concern unless we have very long-lived fish kept in very soft water, or invertebrates living at the top end of soft tapwater fluoridation.

There are various strategies for reducing the amount of fluoride that we introduce to our tanks. Reverse osmosis, of course, but materials that we may use routinely adsorb fluoride. Activated carbon does that and also biological stuff that some here refer to as ‘botanicals’. Because of the geographic locations of the sources that I was reading, most of the references to botanicals were to leaves and bark of Indian-type trees: neem and khair (whatever that is!) for example. But there were mentions of the genus Terminalia (aka Catappa or Indian Almond) and Quercus (oak) as being effective in reducing oxidative stress.

I hope that helps – and apologies to all concerned that I failed to note down the citations for the sources of the above info.

[BigBen]

Thanks Vale!.

As I have soft water, I wonder if they will do something to adjust the hardness slightly. I hope not, but it also appears that there is a lot of scepticism in the council about it, so hopefully they won't put it in.
KH = 2°dH
GH = 3°dH
(Tested at room temperature).
Would a HMA filter remove it? I know the difference between RO and HMA, but struggle when it comes to the water chemistry in knowing what is what. I'd also be a little concerned at how long it takes to produce the water I'd need for my 6 tanks, plus a few more in the future.

[Vale!]

Yes - an HMA (Heavy Metal Axe) filter should remove it, I reckon. Best check on Google, though?

[Edit: I've checked ... and it does!]

[fr499y]

Yep HMA should do the trick

[BigBen]

Cool, thanks! I'll have a look to see if I can work out a new water change regime that doesn't involve moving buckets!

I could have a water butt I guess with a pump in it.

[Vale!]

Yes, BB - that's pretty much the arrangement at Vale! Towers, except that the pump isn't a permanent fixture.

Water butt with two airlines installed (to stir) :




And an immersion heater (stainless steel, not copper!) at the bottom (murky pic but you get the idea!):

[BigBen]

I'd remove the pump when not in use. I'd probably put it in the garage as I can easily make a water supply so wouldn't need to worry about a heater.

How long does it take to fill?

[Vale!]

We have pathetically low water pressure here so it takes yonks. The butt's around 200L and it takes the best part of a day-and-a-half to fill!

That's why I bought an RO pump which makes a dramatic difference (and has better efficiency with respect to waste, I believe).