Quick question regarding pH measuring

[Chris S]

Hey guys,

Just a quick question here.

My fish room is setup using sponge filters, and as such, I am battling high pH problems due to the gassing off of co2 from my water. I'm currently trying to lower it via peat, which has worked a little bit...I think...

Anyway, my question is regarding measuring pH.

I have found using the drops (specifically, API) is yielding me a wildly different reading than my pH meter.

First off, I don't like my pH meter and don't trust it (because I have to recalibrate it EVERY time) - but after recalibrating it, it SHOULD be accurate.

Using the liquid test kits, I find I have a MUCH lower pH level. I am curious if this is due to the process in which I mix (shake, invert) the reagents in that co2 is added, therefore lowering the test result.

Here are some test results I am dealing with right now:


With pH meter:
Tap water: normal pH 7.6, after gassing off: 8.1/8.2
RO w/peat: 7.2

With liquid test:
Tap water: normal pH 7.6, after gassing off: 7.4
RO w/peat: 6.4

What should I be trusting here? Or should I just invest in a high quality pH meter and forget this madness?

 

[Mike Wise]

I find pH meters more accurate than the simple colorometric chemicals sold for aquariums. This, of course, comes with the caveat that the meter is regularly calibrated. If you have a more inexpensive meter, then a better quality meter will be more accurate.

After looking at your readings, I'm curious where the excess CO2 comes from in your tap water? Most tap water is well aerated before being pumped into water pipes, so the gasses in the tap water should be very close to that in the atmosphere. Unless you are on a personal well with a naturally high CO2 content (ala Perrier carbonated water), I would think that the pH would be fairly similar before and after aeration. If this is the case with your water supply, then your chemical test seems more accurate than your meter. I would buy a combination pH/µS/TDS/Temperature meter together with calibrating reagents and probe stabilizer fluid. It will be cheap in the long run.

 

[Chris S]

Thanks for the quick reply Mike.

I think your answer was the one I was expecting. Any suggestions on high-quality, decently priced combo meters?

As for the co2, I have municipally supplied water - so I agree in that it should be low in co2 content to begin with. I think, perhaps, I was looking for reasoning in my readings via the pH meter. The first thing that popped into my mind was the loss of co2 via the sponge filters. That doesn't necessarily make it true

 

[dw1305]

Hi all,
I think the problem is with the pH, rather than the pH measurement. What you have to remember is that pH and carbonate hardness "buffering" are intimately linked, and that in de-ionized water pH doesn't really have any meaning as pure H2O has no buffering, any addition of acid or alkali will cause the pH to drop or rise to extreme values. If you have "buffered solution", and you appear to have, in this case the acid and "conjugated base" are carbonic acid and bicarbonate, and the reactions are:

HCO3(-1) + H2O = H2CO3 + OH(-1) dissolved in water
H2CO3 = H2O + CO2 dissolved in water

Both of these reactions are at equilibrium and reversible. If you add components to one side of the reaction, you drive it in the other direction, so if you add CO2 to an aquarium the pH will fall and if it leaves solution the OH-1 ions will rise and the pH with it.

Mike's suggestion of a multimeter is a good one, this will give you a much better idea of the carbonate hardness ("Buffering") of your water.
CO2 should equilibriate fairly quickly with even if your tap supply is under pressure as CO2 is fairly soluble in water (much more soluble than O2 for example).

As an example rainwater from the water butt at home (Wiltshire, UK) is about 150 microS in the summer, 80microS in the winter. Water out of the de-ioniser in the lab. is about 3 microS, and about 20microS out of the steam distillation unit, pH isn't a very useful measurement for any of these. The water in the tanks is rainwater and I don't personally worry too much about the pH levels, particularly if you don't add CO2 the pH will be changing all the time as the carbonic acid and bicarbonate level equilibrium changes (dependent upon the degree of dissolved CO2 and the respiration/photosynthesis balance). The less buffering you have the bigger the swings in pH will be (in my tank at about 150 microS, pH will be well above pH7 during active photosynthesis and about pH6 before the lights come on).

I do occasionally check the conductivity, because I know most of my cations will be calcium from calcium carbonate dust in the rainwater, and this is a "proxy", an indirect measurement of buffering.

I use rainwater because my tap water is about 620 microS, and a fairly stable pH of 7.8 - 8.0 (it has about 17d carbonate hardness so is strongly carbonate buffered. Figures from Wessex water)
Calcium (milligrams per litre) 119 (298 x 40% = 119)
Calcium carbonate (milligrams per litre) 298
Degrees German (ºdH) 16.7 (16.7 x 17.85 = 298)
Degrees French (ºf) 30
Degrees Clark 21
Sodium (milligrams per litre) 22
Conductivity 615 micro S(iemens)

cheers Darrel

 

[Chris S]

You raise another question that has been on my mind.

Since my RO reservoir effectively has no buffering capacity (0 dKH), I was hoping the peat would have a dramatic effect on the pH - alas, not much change.

Prior to finishing my fish room, I have had great success in breeding apisto's. I've never worried about my pH before either. Now that I have invested fairly heavily on trying to streamline my breeding efforts, I seem to be running into roadblock after roadblock. This is why I am now concentrating on lowering the pH of my water - in hopes to spark off a little hanky panky

Suffice to say, reigning in nature isn't always as easy as one might think!

I appreciate your insight Darrel.

 

[dw1305]

Hi all,
R.O. has no buffering, and the addition of even the weak acids (carbonic from dissolved CO2 or humic acids from peat) should cause the pH to crash.

It may depend upon the type of peat, sphagnum peat is very acid, but fen sedge peats may have a pH above pH7.

If you have a pH of pH8.2, you definitely have a source of bases present in the water (pH is a logarithmic scale, pH8 water contains 10x as many OH- ions (or other anions expressed as OH-) as pH7.

cheers Darrel

 

[Chris S]

Not questioning what you are saying, but from my understanding adding an acid to pure RO won't necessarily cause it to crash. I thought it was more like a putty you can mold to whatever pH you want.

I mean, adding (for instance) peat with a pH of 6.5 should turn your RO 6.5, but not any lower - correct?

 

[dw1305]

Hi all,
Chris it all depends on the degree of buffering, several member here keep their "blackwater fish" in 100% R.O. which has just been peat filtered before use, they don't re-mineralise it at all.

It is certainly much easier to add salts to water than take them away and it is only the combination of low pH, low conductivity and soft water that can reliably lead to the successful breeding of the more difficult species.

Pure R.O. is pure H2O (every thing else we call water H2O isn't it is a weak solution of one or more salts) and H2O is an electrical insulator.
H2O actually consists of H+ and OH- ions, and there are equal numbers of each (pH is a strange measure it is the "negative log of the H+ ion concentration"). It has no solutes and therefore no "buffering", buffers are reserves of their acid and conjugated base. The pH should read pH7 (so basically a ratio of 7:7 H+:OH-) for pure H2O, but realistically it can read nearly anything as any addition solutes will change the pH radically. Our purest de-ionized in the lab will read about pH 4.5 in it's 200 litre aspirator, due to dissolved carbonic acid (from atmospheric CO2), but the addition of a minute volume of a strong base like sodium hydroxide will send the pH soaring to pH9 or higher (pH is a log scale so we have changed by almost 5 orders of magnitude, or 100,000 times moer alkaline )

I'll use CO2 for my "buffered solution", in this case the acid and "conjugated base" are carbonic acid and bicarbonate, and the reactions, (if I use sodium carbonate, (calcium carbonate would be just as good)) are:

NaHCO3 = Na(+1) + HCO3(-1) dissolved in water
HCO3(-1) + H2O = H2CO3 + OH(-1) dissolved in water
H2CO3 = H2O + CO2 dissolved in water

Both of these reactions are at equilibrium and reversible. If you add components to one side of the reaction, you drive it in the other direction, so if you add CO2 to an aquarium the pH will fall . This is also why hard water resists pH changes much better than soft water, and we re-mineralise R.O water achieve a reserve of buffering (or carbonate hardness - KH).
My Corsham tap water, Lake Malawi, Lake Tanganyika and "the Sea" are all almost infinitely buffered, and their pH will remain almost constant. Conversely many of the S. American "black waters" have no measurable hardness at all, and conductivities below 20 microS.

From Linke and Staeck "American cichlids 1: Dwarf Cichlids"

Lago Ara on the left bank of the Lower Rio Negro pH 4.3, total hardness, carbonate hardness both less than 1, conductivity 10 micro. S.

cheers Darrel

 

[Chris S]

Thank you Darrel. Quite informative

This should help me down my road here!

 

[Chris S]

Ok, well to update...

I'm using a milwakee SMS122 pH meter now (as opposed to the handheld meter I was using). After pulling it out of storage to recalibrate it - it is still dead on. 7 and 4. So, I'm going to go ahead and trust the readings.

The readings seem more accurate too:

Tap: 7.6
RO w/peat: 6.2

Now that seems better, no?

 

[dw1305]

Hi all,

RO w/peat: 6.2

, that sounds about perfect.

You should be able to get that further down with an addition of weak acid, humic or carbonic acid for example and add buffering and KH with a small amount of sodium or calcium or magnesium carbonate. If you want to raise the GH and not the KH you can use magnesium sulphate.

I'd probably have a play with oak leaves or oak bark in the tank and see what the pH drifts down to. A conductivity meter would still be very useful however.
It would be the one bit of kit that I would buy and use.

cheers Darrel

 

[Rod]

Sorry

I've had a Good night!

but with relation to ph

Please....

What fish lives in Hard acid water...?????

What fish lives in Soft alkaline water...???





NOT MANY!!!!

If you want low ph.....make the water soft first....:biggrin:
If you focus on ph and ignore hardness...TDS ....then you are missing the point....you are just targeting a truly meaningless number

just my drunken opinion!

 

[Chris S]

Yea, I'm still interested in getting myself a good multimeter. Right now I just have a TDS meter and pH meter(s!!), plus the usual liquid test kits.

As for the hardness, I'm using RO so I've been keeping my tds around ~50.

 

[viejo]

So what pH meters do you guys recommend? My present meter is unreliable @ best.

 

[Chris S]

I was going to look into trying to find this meter locally:

http://www.instrumart.com/Product.aspx?ProductID=24866

Hanna HI 98129 pH/temp/EC/TDS meter

 

[dw1305]

Hi all,
Hanna are a good make of meter.

As to Rod's question, it is a good point. "Soft" (low carbonate hardness), "acid" (low pH) and low TDS (low electrical conductivity) all most always go together (and this is the type of water which the majority of Apistogrammas are found in).

You can have soft, alkaline water, it is more unusual than hard, alkaline water, but it does occur.

This is because GH is the combined Mg(+2) and Ca(+2) content of your water, and is how hard your water is, whilst KH is the "Alkalinity" and measures the carbonate content -the KH buffering (of pH) capacity of your water.

So sodium bicarbonate would raise conductivity (from the Na+ ions), and KH (from the HCO3 ions), but not GH (Na+, but GH measure the multivalent ions Ca2+ etc.), and Magnesium sulphate would raise GH (from the Mg2+ ions) and conductivity from the Mg2+ ions, but not KH (SO4- ions don't add carbonate buffering).

Examples of animals from these unusual water are the Sulawesi shrimps and Snails from lakes Malili & L. Poso, and even Lake Victoria is very different from L. Malawi and L. Tanganyika, it has a pH of up to pH9, but only 2 - 8 dGH.

cheers Darrel

 

[Mike Wise]

I've used the Hanna 98129 for several years. I even took it on a 4 week collecting trip to Peru. It got bumped, jostled, and totally submerged on occasions. It worked - and still works - flawlessly. Just remember that for accuracy you need to buy the calibration standards and calibrate the meter every month or two. I use the sachets. In this way, I can't contaminate the reagents in a whole bottle. I also recommend the electrode storage solution to extend the meter's electrode life.

 

[Chris S]

Thanks to both of you, again, for your input.

 

[Rod]

Thanks for the question Chris

Some Good information provided

Thanks Darrel.....Dario species are another fish best kept in soft alkaline water
certainly out of the norm!

 

[dw1305]

Dario

Hi all,
Thanks Rod, you must be a mind reader because I spent a long time looking at some Dario hysginon last night, before concluding they were all males.

I've just read this

pH Range - prefers neutral to alkaline water with a value between 7.0 - 9.0. Hardness - The water in northern Myanmar is typically soft despite the relatively high pH so aim for somewhere within the range 1 - 5°H."

Although D. hysginon may not be a cichlid (all though they are Perciformes), they certainly are dwarf and they definitely think they are cichlids.

cheers Darrel