click pic to enlarge Pelvicachromis taeniatus 'Nange' photo by MFJacobs 2004	click pic to enlarge Pelvicachromis pulcher photo by MFJacobs 2004	click pic to enlarge Pelvicachromis pulcher photo by MFJacobs 2004

by Mike Jacobs
“That fish died from pH shock . . . I’m sure of it!” How many times have you heard that story, as though it was an act from 'above' that couldn’t be avoided or controlled and certainly no one was at fault? One of the basic tenants of tropical fish keeping is at work here . . . the “old wives' tale”. That is the scenario when you get a new fish from a retail store or a friend..."...be careful because the fish will go into pH shock in a hurry and may never recover if the pH of the two different water sources are different”. I have been hearing that for almost 50 years and in fact have been guilty, at times, of spreading the word according to the “old wives'” for some time now. But something didn’t ring true! The pH rumor really seemed, at times, to make a great deal of sense. I mean, I always knew that going from a pH of 6 to a pH of 7 is not a difficult task, and that actually it is not an increment of 1 as it would seem to be . . . it is a power of 10 because of the scientific definition of pH (pH scale: 1-14 with 7 being ‘neutral’ but it is not a linear scale it is a negative log scale of the concentration of the [H+] (hydrogen) ion . . . each unit is a power of 10. The technical discussion of pH is for another article!) and that kind of increase, a power of 10, of anything would seem to be enough of a change, to bother, even to damage most any living organisms doesn’t it? However, the only discussions I could find involving pH and damage to tropical fish was that going from a lower pH to a higher pH dealt with water that contained ammonium (old over-stocked water and the pH had been driven down) and the fish in that water was taken home and put in a higher pH situation and BINGO…the ammonium becomes ammonia and the skin and gills are burnt BIG TIME (again...another article)! So . . . Nada . . . pH is not probably the cause of fish problems assuming your fish store keeps reasonably clean water conditions. In fact, what the real killer of newly introduced tropical fish is most likely the change in Total Dissolved Solids (TDS) of the two volumes of water. To help explain this phenomenon we will have to go back to 9th grade chemistry and equilibrium and diffusion and osmosis. Be patient...at least there won’t be a test tomorrow! Sit tight, and I will, I think, convince you with a little bit of scientific “sluthery”...I made that word up . . . that it is NOT a 'pH shock' killing those fish but in fact a change in TDS!

Equilibrium: steady . . . non-changing . . . well . . . OK . . . but let’s really get ‘down and dirty’ with the scientific people and discuss equilibrium from their viewpoint! There are really two types of equilibrium. Static and Dynamic . . . they are not difficult so before we get into the real “stuff” here lets get these two principles out of the way so we can all be on the same talking plane . . . this won’t be tough . . . honestly, stay with me for a while!

Static vs. Dynamic Equilibrium: Picture a bucket of water . . . the water level is constant and no water is entering the bucket or leaving the bucket in any manner . . . the water is at “Static Equilibrium”. At a molecular level, the molecules are moving around, for sure, we learned about the molecular movement in 6th grade, but the water, with regard to the bucket it is in a state of Static Equilibrium. ARG-ARG-ARG!!! . . . NOW, the bucket springs a leak . . . the water is no longer “Static” . . . in fact no longer at equilibrium the water is leaking out. Ok, don’t panic, I have a hose . . . lets put the same amount of water in the top of the bucket that is running out of the hole . . . ah-hah Batman! . . . “Dynamic Equilibrium”...two opposing actions occurring at the same time to produce an equilibrium . . . water in / water out . . . same level . . . “Dynamic Equilibrium”. Don’t you feel smarter, now????????????

So far not so bad . . . go get a soft drink and turn off the television now . . . it gets a little bit tougher, but still . . . it will be OK!

Diffusion vs. Osmosis . . . what happens during diffusion/osmosis? It’s really very simple and it absolutely applies to tropical fish and their body cells in particular their gill cells, and it’s the reason you’re reading these notes, but osmosis seems to be contrary to what most people think is natural so it takes a tad bit of thinking to grasp the concept . . . but its because you’re thinking diffusion and don’t know how or why osmosis works . . . as a matter of fact you might say osmosis doesn’t work. Let’s try and knock the mountain down to a mole-hill here.

Diffusion: You have a beaker of good clean clear water . . . you put in a drop of ink into the water. It pretty much stays in a blob for a second or two but then the molecules of the red ink start to spread out and eventually “diffuse” . . . that’s diffusion . . . and eventually folks, the ENTIRE glass will become a shade of the color of the ink, a diluted color of the ink, for sure, but the color of the ink. The reason it will happen, the diffusion, is that the water molecules are in motion in the beaker of water. Even though there is nothing going on with the beaker . . . static equilibrium (see how smart you are) . . . the clear (water) molecules are moving and moving and they are bumping into the visible ink molecules and bumping and bumping and bumping until the ink molecules are spread equally around the entire beaker just like the water molecules, and the beaker has entirely taken on the tint of the ink . . . there are all kinds of reasons for the speed of diffusion, heat for one . . . but that is “DIFFUSION” (picture 1).
(picture 1)

Little step . . . little step . . . Ok . . . take a drink of that soda . . . !

Now, diffusion can also happen if there is a “membrane” separating some water from some more water (picture 2). A “permeable” membrane is a barrier that has minute holes of such a size that all of the molecules in the fluid will fit through the holes . . . see, not so tough! This barrier (membrane) is put in place so that the molecules can only go through not around the membrane (barrier) . . . what happens? The drop of red ink is again put into the clear water. A molecule of the red ink bangs against the barrier until it finally hits one of the holes and BINGO, it’s now on the other side of the membrane . . . the movement of the ink molecules . . . and all the other molecules . . . would look almost like the drop of ink in the beaker without the membrane. The process of diffusion would continue, although slower, just like the movement of ink in the last example until all of the water would again be the same color, although a little less dark than the original red ink . . . thus the molecules went from a more dense (dark red) to a less dense (light red) situation . . . DIFFUSION . . . of course we remember that even when totally diffused, at the molecular level there are still ink molecules going through the holes of the membrane . . . it’s just that they are all going both directions at the same rate and time, ALMOST, and it “looks” as though nothing is happening . . . remember, at the molecular level there is always movement . . . one-two-cha-cha-cha! (picture 2)

(picture 2)

See...not so bad so far, huh...!!!!!

OSMOSIS: Well here’s the slam dunk . . . no, no . . . it won’t be so bad . . . just go get another soft drink!

Osmosis: (definition... www.dictionary.com) Diffusion of fluid through a semi permeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal concentration of fluid on both sides of the membrane,
(Further definition... Wright Huntley) until the pressures on the two sides produce a static equilibrium condition and water is flowing both ways at the same rate.

Problem . . . If all the cells in the body of a human or fish had “permeable” (lets every molecule through) membranes then we would be in big time bad shape . . . all of the gasses and fluids in the world would be allowed to go right into or out of and around the body. So the “semi-permeable” membrane was invented. What happens in this case is that the holes are big enough to only allow certain sized molecules through the barrier . . . but keep others out. Depending on what the cell was intended to do the size of the holes varies to let different molecules 'in' or 'out'. Well let's look at this situation.

You thought you were reading about fish didn’t you . . . heh, heh, heh!!! . . . take a drink of that soda!

Let’s approach this from around the bush instead of the front. Picture this . . . you and I have a game going . . . we are in a handball court with a clear wall dividing the court in 2 sections and you are in one section and I am in the other section. The idea is to throw balls through holes that have been drilled in the clear wall between you and me. We can’t throw them over the wall and we can’t throw them around the wall. All of the balls are the same size and the holes in the wall will permit all of the balls to go through the holes and once the balls start moving they never stop . . . both you and I are equally adept at throwing and have all of the physical skills necessary to compete against each other . . . after a while wouldn’t you think that there would be as many balls going through the wall one way as the other????? . . . sure . . . all things being equal of course. Well, lets share a final thought before I change the rules . . . the balls are bouncing all everywhere . . . off of each other and the walls and bouncing and hitting and going through the holes . . . the balls are everywhere, on both sides of the wall and filling both rooms . . . diffusion is what is happening in our game! Now let’s change the rules . . . we start the game over but on your side of the room there are some balls thrown in that are already moving and floating and bouncing around . . . generally these balls are going to be a pain to you . . . these new balls on your side will not fit through the holes in the clear wall that we are throwing at . . . too big . . . much too big! OK . . . the game starts . . . you start throwing, I start throwing, and we all start throwing...what probably is going to happen? Well nothing on my side will change . . . I’m having a ball (so to speak) . . . but on your side something is obviously happening, actually two (2) things are happening . . .

1) The bigger balls are blocking your smaller balls from going through the holes . . .
2) When my ball goes through one of the holes it is blocked from coming back through the holes by some of the bigger balls on your side

. . . whether thrown by me or being hindered from your throws on your side . . . more balls will be and stay or your side than you can possibly get to my side . . . and picture this . . .the more big balls you have in your side of the room faster will be the influx of my balls into your room because the more big balls on your side the more holes will be covered up by the big balls and your little balls can’t get through very fast at all . . . folks, that game illustrates a “semi-permeable” membrane, with one side . . . yours having a higher TDS (Big Balls) than the other side so some molecules will go into the side of GREATER concentration . . . not to the side of lower concentration like Diffusion and so in a “semi-permeable” membrane situation, just like the game, the flow can go in the opposite of Diffusion if the two sides of the membrane are of different TDS (picture 3).

picture3

OK, OK, OK . . . so what . . . well, here is what that produces!!!

Picture a cell on the gill of a fish . . . it has a concentration of molecules in it that the body likes and enjoys and the surrounding water is of the correct TDS and all is adjusted (slow flow of molecules through the membranes of the gills)...you net the fish and put them in a tank water that is of LESS TDS (softer water) than before (the big balls are in the inside of the gill cell)...the water molecules are going to start going INTO the cell (in the same way I was beating you in the game) until the point that the cell can no longer hold the water . . . the cell actually will then burst *depending on the amount of TDS difference in the fluids) . . . yep . . . there’s the problem folks!!! The cell membrane will actually burst before the body can make the adjustment . . . it can all happen that quickly! (picture 4)

picture 4

That, folks, illustrates the problem of changing a fish from one set of water parameters (high TDS) to another (lower TDS). That’s right folks. From a higher TDS fluid (water) to a lower TDS you are actually bursting the membranes of the gill cells (and some on the body) and if that in itself does not harm the fish by causing immediate breathing problems, if too many cells are ruptured, then most certainly there is now an entrance for bacteria at the point of eruption.

'Osmotic Pressure Shock' is what just happened here, folks . . . not pH shock! It was a failure of the osmotic regulatory system! Well, it's not a 'failure' really; the osmotic regulatory system simply couldn't make the change quickly enough. The system will for sure make the change if the fish is alive; but has the fish been too badly damaged to quickly becomes the point?

Well, how about the other direction. From a lower TDS to a higher TDS . . . yep, problems there too. However, the body seems to be able to fend off this problem a little better. Using our game, what is happening is that the water in the cell will move to the outside of the cell membrane . . . dehydration! Not as serious as a ruptured cell but certainly could cause some difficult breathing problems depending on how many cells were involved and to what degree the dehydration happened, but the ability of the body to recover from this malady seems to be much greater than the opposite problem.

Ok, just what is going on here?

The old “pH shock” syndrome is not the problem it was once thought to be. Even Jorgen Scheel, in his Killifish Atlas in the 1970's spoke of changing the pH on killifish by 3 pH units and there was absolutely NO EFFECT! I can see the reason for the old “wives'” tale . . . generally, I think, back in the “old” days pH was much easier to read than hardness, and a lower pH is generally associated with lower TDS, it was probably assumed that pH was the culprit to the problems of new introduction of fish. It was a mistake! It was a mistake that even I “told” over the years until I began to listen to some people who made sense, and then I went to the books. It has been and interesting journey finding that there seems to be no basis in fact that fish put in water of great pH difference will have a problem with survival, but rather, that very elementary biology illustrates quite clearly and quickly leads us to what happens to our fish given a drastic and sudden TDS difference (hard water to soft water). But now you too know what the problem is . . . this new knowledge has opened up 20 new questions for me . . . back to the biology books...see if you can now tell me what “Reverse Osmosis” means . . . think about it. I’ll explain all of that next time!