PH isn't hardness. So why does my buffered water so easily give false low readings?
I know that a correct pH reading is taken after just a gentle swirl. But I thought that hard water would be more fortified against CO2-induced pH drop. It's just as susceptible as my non-buffered 0 hardness tap water. I shake either test violently and the reading quickly and easily drops to the lowest reading on the color chart. That tells me that my water is not adequately buffered. Even the tank that has a pH of over 8 caused by crushed coral is easily defrauded into below 6.0 with a simple violent shake and breath of exhaled air from my lungs into the tube. What is going on? Why is it so easy to fool the hard water into accepting so much CO2?
The resistance to change in pH, the "buffering capacity" is not related to the ability of a liquid to dissolve a gas in solution (partial pressure of a gas in solution). However, the CO2 once in the water will convert to carbonic acid in water, at least some portion will - that's why a gentle swirl and not a shake is needed. More agitation=more CO2 dissolved from the atmosphere into the water. You are correct, harder water with more minerals does have more buffering capacity than DI water. The minerals will tend to combine with the hydrogen ions given off by acids and buffer against pH change. CO2, actually the carbonic acid, can rapidly acidify a system and can overwhelm the buffers. Remember that CO2 is at relatively low levels in the atmosphere and even lower in fish tanks. The carbonic acid in your tank water can interact over your substrate, giving the tank as a whole a much higher buffering capacity than a small sample of water from the tank. Your breath also has a great deal higher CO2 than the air overall.
I'm certain a chemist can make a more accurate explanation, it's been a long time since I took inorganic chem!
That's a good reply. Thanks for pointing out the difference in atmospheric air vs. lung exhale and water quantity. It appears the picture in my head is still far from accurate concerning pH and hardness. I thought that moderate hardness was a great warrior against pH crash, and now I know that it is, given the normal scenario of an aquarium setting. But now I realize that gas content can create pH readings greatly below hardness levels.
Now, for fish health, do you think it would be better to allow them to live in a stable low-pH, low hardness environment that occasionally endures a rapid increase and decrease in CO2 gas (and pH thanks to the gas factor) OR would it be better to continue buffering for hardness knowing that I'm never maintaining it with true consistency week to week as my coral dissolves and has to be replenished from time to time? Which is the lesser evil? Living in very soft, stable (but vulnerable!) water with a CO2 swing now and then, or living in water that has differing levels of hardness depending on a myriad of maintenance factors? I've been using coral for years and it has always eaten at me knowing that my hardness fluctuates on water change day and if I go too long without changing the water.
To properly answer your last post, we need to know more about your fish and tank. What are the fish species, how many, what tank size, are there live plants, what is the pH of the tap water and the tank water, and what is the hardness of the tap water?
Coral is not the best "buffer." Also, pH fluctuations are perfectly natural in nature and they occur in every planted aquarium over a 24 hour period. Sudden "crashes" are what we want to avoid, but they are rather unlikely in most situations. This we can sort out with the afore-mentioned information before us. Good response from DKRST to the initial question.
Tank is 55g. Current inhabitants are a somewhat frightening list until you learn most of these fish are babies in the 3" to 4" range or smaller. Here is the list:
Adult zebra angel, about dollar coin size, and thin.
Two green mollies, female 3", male 2" (these would be moved out if they show signs of stress or at first opportunity)
One 3" brachyrhamdia meesi
One baby gold dust bichir, 4" and thin
One baby acanthicus adonis, 4" without tail, chubby and growing
One platysilurus mucosus/malarmo, 5" (nothing known about care of this fish, data does not exist)
One giant betta, 2.5 inches
One satanoperca leucistica (or whatever they are called this week), 5" and a slow grower at that.
The main contributor to bioload is the acanthicus adonis.
I had live plants but the pothos, spider plants and willow branch seem to have starved them and they have been discarded as they were just decomposing slowly rather than growing. I don't want a bunch of nasty plants anyway, just clean water please.
Tap water has no reliable hardness. GH of less than one.
I don't like using coral as I've noticed it is inconsistent week to week. It shows up a dollar short and a day late to provide some buffering after the stress of the water change has already been endured.
I'm not worried about pH fluctuations due to CO2 swings anymore. I was, but after finding some better info I am now only worried about hardness depletion and how minimalistic my buffering regimen should be. Epsom salt and a little calcium chloride and magnesium via crushed chicken egg shells?
I change 50% of the water per week but am about to step that up since the adonis is catching up with me and nitrates were actually 40ppm last week. Eek! So two 50% water changes a week ought to make it pretty much impossible for the emersed plants to eat up all the minerals and salts in solution, right? I mean, the solids present in my tap aren't much to begin with, but I would expect a tank would need more neglect than mine to have a genuine crash of noteworthy proportions, right?
What is the GH in the tank?
Changes from week to week. Measured it once or twice and realized I was just chasing a dragon trying to get it stable. Don't remember the number anymore. Can't find the test, either. Might have to buy one.
The water report is incorrect. They think our pH is in the 8.0 range but even fresh out of the tap with gases trapped it's only 7.3 before degassing. I currently check my pH constantly, though I'm now realizing I've been misled and need to be watching my hardness more than my pH. Like i said, GH is less than 1 (that's testable and verified by the water company), pH is usually 6.5 or lower after degassed. With such a low GH, all it takes is a bubble wand in the aquarium to change the pH reading of a test kit.
http://www.ci.everett.wa.us/Get_PDF.aspx?pdfID=3799 Page 5
Copy and paste from PDF, had to alter it to fix format.
Alkalinity3 ppm 17.5
Aluminum3 ppb 0.016
Calcium Hardness3 ppm 8.9
pH3 s.u. 8.0
Sodium4 ppm 6.2-7.1 6.8
Total Hardness2,3 ppm2 9.1-13.3 11.3
2 Hardness and alkalinity units are in ppm as CaCO3 (calcium carbonate
3 Results are from samples collected from 26 locations in Everett’s distribution
The water in my aquariums has varying GH because of crushed coral and the way is dissolves inconsistently week to week.
Those numbers indicate very soft water, comparable to what I have north of you in Vancouver, BC. This means that the natural acidification of aquarium water will allow the pH to lower easily. This is because there is little hardness, especially carbonate hardness (KH) which would if higher tend to buffer the pH.
If you have soft, acidic water fish, this is not much of an issue. If you have livebearers, rift lake cichlids or any of the hard water species, they will not last without modifying the water by adding calcium and magnesium to raise the hardness (and corresponding pH).
Adding CO2 to water adds acid so the pH falls. As there is no buffering capability to speak of, it will fall easily, as you've noticed. When testing the tank water for pH, gently mix the regent with the water in the tube and read it immediately.
Has this helped?
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