digital meters..

[dw1305]

Hi all,
Mike is right, the fish have evolved in water which have virtually no dissolved salts, and these are often the conditions black water fish need to breed successfully.

Also, if you dont mind, i am not quite sure I understand conductivity and how it relates to fish health? I understand pH, hardness, and obviously temperature, but what are the ramifications of too high or too low conductivity?

I'll have a go at this, pure H2O is an electrical insulator, what we call "water" is actually almost always a dilute solution of salts. This is why adding compounds doesn't help, it raises the TDS. We can add enough acid to counteract any amount of alkalinity, but we are getting further away from H2O all the time. We can only get more suitable water by removing (RO water) or exchanging (Ca2+ etc. for 2H+ in humic compounds) ions.

The relationship between compounds in the water and conductivity is shown by this graph, you can substitute any salts for NaCl, and for weak acids, like the humic acids from Indian almond leaves, peat or alder cones we can assume it will be the linear section of the HSO4 graph.

Whilst conductivity tells you how much salts you have, it doesn't tell you what they are. This is where pH comes in, the pH is a measure of the ratio of OH- ions and H+ ions (H + H + O = H2O) (or other acids and bases expressed as OH- and H+ ions). The easiest way to think of it is that acids are H+ donors and add H+ ions, and alkalis are H+ acceptors and remove H+ ions.

At the ratio of 1:1 H+:OH- the pH is pH7 (really it should be pH-7 (10-7 H+ ions)), more H+ ions are added and pH falls (more H+ added, at pH6 H+ = 10-6). Because we are dealing with powers to the base10, pH is a base10 log scale and pH5 is 100 times more acid than pH7, and pH4 1000 times.

So pH tells us the ratio, but not the amount. If you think of scales that are in balance, this is pH7. That balance could be that we have 10Kg in either scale or 10g, pH doesn't differentiate. If we add 10g of "acid" to the 10kg scale, we will have changed the balance very, slightly to the acid side, and the pH will fall, but only slightly to the high pH6 range. We can think of the 10Kg in the alkali as our "buffering". If we add the same amount (10g) of acid to our 10g scale, we now a ratio of 2:1 acid:alkali and our pH will drop much further and much faster.

This is the scales for well buffered alkaline water, but it shows the principle.

cheers Darrel

 

[regani]

Also, if you dont mind, i am not quite sure I understand conductivity and how it relates to fish health? I understand pH, hardness, and obviously temperature, but what are the ramifications of too high or too low conductivity?

It has to do with how the cells in the body of the fish work. A certain concentration of salts and a certain pH is required inside the cells for them to work optimally. To keep all the contents inside a cell, the cell is surrounded by a membrane and there is only limited exchange with the outside, usually through specialized pores and some transport units that make sure that nutrients get inside a cell and waste gets out, they also maintain the concentration of salts and pH inside the cell.

The problem with this an effect called 'osmotic pressure'. Basically, if you have salt solutions of different concentraions next to each other seprated by a membrane where things can move through freely, after a while you will observe that the salt concentrations on both sides have become the same. If you restrict the movement of ions through this membrane, but let the water through freely, this drive to even out the concentrations is still there, but now the ions can't move through the membrane. so the job of trying to even out the concentration is left to the water molecules alone. they will move to the side of the membrane with the higher salt concentration, trying to dilute it. as a consequence the total volume of water on that side of the membrane increases, which means in a restricted volume the pressure increases, which can be measured.

In case of the cells this effect can be seen under a microscope quite clearly: if cells are placed in a solution where the concentration of salts is higher than in the cell, the water molecules will try to even things out (because the movement of ions through the cell membrane is restricted) and move out of the cell to 'dilute' the outside; as a consequence the cell shrinks. if the cell is placed in a solution where the salt concentration lower than inside the cell, the water molecules on the outside will move inside the cell, again trying to make both concentrations the same; as a consequence the cell expands. this osmotic effect can go to extremes, e.g. the cell can swell until it bursts and dies.

Evolution has provided the cells with some tricks to partially compensate for differences in salt concentrations, but there is an optimum range where this works and outside this range the cell may not be able to fully compensate and gets damaged.

if the fish species has evolved in water with very low salt concentrations (soft, low conductivity water) the cells will have adapted to these conditions and are much better equipped to keep water out and salts in, than cells of fish that have evolved in high salt water where it will be more of a problem to keep the water in and the salts out.

of course there many different types of cells in a fish and the skin a a specialized organ designed (amongst other things) to prevent the environment having an immediate impact on other cells in the body and there are other factors that come into play as well (e.g. uptakem of minerals and trace elements through the skin), but the above is the the basic reason why soft water fish don't do well in hard water and the other way around.

 

[gerald]

As I understand it, the salt ion concentrations within the body cells of a blackwater fish and a Lake Tanganyika fish are really pretty close. The important difference is how efficient the ion-uptake cells are in the gills and gut, and how efficient their kidneys are at excreting water without losing salts (very dilute urine). Blackwater fish gills and intestines are adapted for absorbing all the Ca, Na, K and other ions they need from the water (and/or food) at ultra-low concentrations, and their kidneys are super-efficient at excreting water while retaining most of the salt ions. If these ions are way more abundant in the water than the fish would naturally enounter, some species of obligate blackwater fish dont seem able to slow down their ion uptake, or else increase the ions in their urine, so they end up retaining too much salts in the cells. Some other blackwater fishes dont seem to have this problem and can change their ion uptake and excretion rates to live in water with higher ion concentrations. The N.Amer banded sunfish is a good example: In nature they mostly live in very soft blackwater down to pH 3.8, but they can also live and breed in neutral, moderately hard water. (You dont find them there in nature because other species outcompete them).

 

[gerald]

That's what I like about the IQ-Systems ISFET pH meter: Dry storage and very quick to switch on and use, compared with traditional glass probe meters. As close to "dip-and-read" strip simplicity as you'll get with a pH meter.

Ha. Seems that these digital meters are a lot more complex than I was expecting. Guess if I wanted "dip-and-read" I should have gone to test strips and accepted the inaccuracy of them. Probably be at least another month or so before I can splurge on this. I'm sure I'll have questions then.

 

[JasonC]

Thanks to all for the explanations... fabulous posts that were well written and relatively easy for me to wrap my head around. Great information again! There is so much to learn, its overwhelming sometimes.... but still fun. ;P

 

[slimbolen99]

Good read. I have a followup question.

So, if I am wanting to buy the Hanna Instruments HI 98129 pH/Conductivity/TDS and Temperature Tester, the only other things I need to purchase to use this are:

Hanna Instruments HI 70300M Storage Solution for pH/ORP Electrodes, 0.23L
Hanna Instruments HI 7007M 7.01 pH Buffer Solution
Hanna Instruments HI 7004M 4.01 pH Buffer Solution

 

[wethumbs]

I highly recommend buying each of them separately. A conductivity/TDS meter will last a lifetime with frequent battery change and occasional calibration. A temperature tester will also last a lifetime with occasional battery change. A pH meter will only last 1 to 2 years before the probe head goes bad. In fact, I just got my brand new 'El cheapo" Milwaukee pH600 from Amazon for $21.99 to replace the one I bought over a year ago. For pH meter, you will be buying a new one before you need to change batteries.

Milwaukee pH600 just need to be kept in tape water. Just make sure you dont let the probe head goes dry or you will be buying another one.
I use 45uS calibration fluid from Pinpoint for the conductivity meter. You can also get the 53mS fluid if you will be working in that range. I have my Pinpoint conductivity meter for over 20 years now, the last time I check it was only 5 unit off and I didnt even bother to adjust the screw (too much work, it needed a really small flat head screwdriver). As for pH calibration fluid, I have the 4.0 and 7.0. I use it to tell me if the pH meter is bad rather than actual calibration.

 

[tjudy]

Storage solution is usually just a low pH calibration solution. I use the same 4.01 pH solution I use to calibrate the meter.

 

[Mike Wise]

Other than a calibration solution for e.c., these are all that I use for the meter.