pH fluctuation hardness around 3
I'm not particularly worried about this and wouldn't consider it a "problem", but I am curious as to what occurred (or is occurring) to cause this change in pH.
First, some background: 43g tank (actual water content), Flourite sand substrate, moderately planted (8 or so Echinodorus sp., a small bunch of H. leucocephyala, lots of anacharis, 2 anubias), 3 pieces of driftwood: 2 mopani and 1 Malaysian (two were new 2 months ago), and 11 corydoras catfish. DIY carbon dioxide, HOB filter (keep water level high to minimize CO2 evaporation), temp 80 degrees. Currently use Flourish as only plant fertilizer, dose 2x/week; I do 40-50% water changes every 1-2 wks. Tank has been running for about 2 months.
Ok. So, for the first 6 weeks or so, my levels were as follows:
pH: 6.4-6.6 (A.M.), 6.8-7.0 (P.M.)
NH3, NO2: 0
gH: 2, kH: 1-2
So I dosed baking soda at each water change to raise the kH up to 3 because I was afraid of rapid pH swings. When the kH was stable at 3, it was rare to see a pH lower than 6.6. When the kH was 1, pH was a little too unstable for my liking; in the A.M. it measured under 6.4 once.
Now, for the last 2-3 weeks, my pH and hardness levels have been considerably different (all other levels same).
gH & kH: 3 (without dosing any baking soda after water changes).
Like I said, I'm not really worried about it. The fish seem fine and act normally. It's just odd to me. For 6 weeks I had to raise my extremely soft water to stabilize the pH and now I've got pH around 7.4 in the A.M. before the lights are on?! It used to regularly be 6.4-6.6 in the morning and 7.0 in the evening.
So, what's going on? Does this have something to do with my tank or is it my city's water supply that's changed? Unfortunately, I don't think I ever tested the hardness of the water right out of the tap (until yesterday, when both were 3).
I'm puzzled. And I must admit I miss my soft, slightly acidic water. It was nice. But, again, I won't mess with it...I would just love to hear anyone's opinion on what may have caused the sudden change.
I would want to know the reason for the sudden pH rise; that is one full degree, which may be fine for the fish if it does not change more/again, but depending what is causing it, if it starts fluctuating it could spell trouble.
Assuming you have not added anything calcareous to your tank--more on the sodium bicarbonate momentarily--this may be something in the municipal water. Have you tested the tap water itself for pH, previously and now? [Let it sit overnight if you test it yourself, to allow the CO2 to dissipate for a more accurate reading.] If the tap water is also different, I would contact the water people; some have websites. It is not unknown for municipal water authorities to add this or that to the water in order to raise pH.
Another explanation is the CO2. This would normally lower pH, and with a low GH and KH in the source water, CO2 should lower it quite substantially. If something malfunctions with the CO2, the pH could suddenly rise again. There is a lot to all this. Again, knowing the pH of the tap water would help. I would also ask why you are adding CO2? Is it just to lower the pH?
It may well be the build-up of baking soda. I wouldn't use it. Dr. Stanley Weitzman wrote in an article on preparing soft water for characins that sodium bicarbonate (baking soda) has no effective buffer action and cannot stabilize pH in the face of additional acidic waste products. Also, he writes, one must not continually add sodium bicarbonate to adjust the pH because eventually the sodium ions present will reach intolerable levels. As I mention below, I use dolomite to buffer, and would recommend this if you deem it necessary; a very small amount is needed, and it adds calcium and magnesium to harden the water and raise pH simultaneously. In my 115g about half a cup in the filter adds 1.5 to 2 dGH and it works for months and months.
Back to your aquarium, the diurnal shift in pH is normal in planted aquaria as it is in nature. During the day, plants photosynthesize and use CO2, thus removing carbonic acid (which is naturally being produced by the biological actions of fish and bacteria) and the pH rises. The increase in oxygen produced by the plants also binds minerals and organics, further increasing the pH. At night, the CO2 naturally increases [you should not operate a CO2 diffuser during darkness for this reason] and it binds with minerals (calcium) and organics, which raises hardness [depending upon the GH and KH initially] and pH. This occurs in all natural waters and fish have no problem with it; in the aquarium it is of course often more dramatic, due to the larger number of plants in relation to the water volume. And adding CO2 should keep the fluctuation less than without. In my heavily-planted tanks (with no CO2 diffusion) I have a diurnal fluctuation of around .3 to .4 daily.
A comment on another point you mention, the pH below 6.4. This is not a concern provided the fish are soft acidic water fish. I have aquaria of mainly wild-caught SA and SE Asian fish, occurring in natural waters having near-zero GH with pH values from 3 to 5, and they have no problem in my tanks that have a pH of 5 (or perhaps lower, I can't measure below 5). I let the tank drop to whatever it wants. I do buffer the 115g, to maintain a GH of 2 and pH around 6-6.2 but that is all.
When I know your tap water pH numbers, I may have more. Hope this helps in the meantime.
First, sorry I've been MIA and haven't responded before now...working :)
Second, I'm sorry also that I do not yet have an answer to the pH in my tap water question - I forgot to set aside a sample last night to test in the morning. I will do it tonight and report tomorrow AM.
So...other answers. No, I haven't added anything calcareous to my tank that I know of; I haven't added anything to it at all except the corydoras catfish (bony sketelon = calcareous? :-P hihi...)
Thanks for the info about baking soda...I will not use it anymore and if I find myself with the extremely soft water again I will think about dolomite to buffer. I just did a 60% water change the day before yseterday and will do another next week; we'll see if that removes most of the residual products from the sodium bicarb. At least I'll be back to square 1 where I can see if the NaHCO3 was the cause of the pH fluctuation. I was worried when I first noticed it but since the fish seem fine I've become less worried...but still want to figure it out. They are hardy little beasts, my corys - I actually think most if not all were wild-caught.
I know the diurnal shift in pH is normal - it's never more than 0.2 or 0.3 - it's this wild increase that's weird. Even now, there is still a diurnal shift - 7.4 in the A.M. and 7.6 or so in the P.M. To answer your other question, I use CO2 mainly to achieve slightly more acidic water. I balanced everything before ever adding the fish - the pH was around 6.6 when I first set up the tank with plants. In the past (like, over 6 years ago), my water was exactly 7.0 out of the tap, and went a bit higher as the CO2 dissipated - I think the typical number was 7.2 in my old tank back in those days.
I do keep fish that come from soft, slightly acidic waters (corys now, later I'll add a school of cardinals and maybe that's it...maybe another characin, but all fish from soft, acidic waters). I was kind of happy about having water with a pH around 6.4-6.6 and super-soft...but I'm worried about the dramatic changes.
Enough yacking from me now...thanks very much, as usual, for your valuable input. I'll get back to you with the pH of my tap water. I wish I had tested it 6 weeks ago as well. We'll see what happens after I do another water change next week. Maybe it's the bicarb that's messing with it all. If it ever goes back to soft and acidic, I'll try to buffer the hardness at 2 using dolomite. How much does it raise the pH? I'm sure there's a formula for that somewhere... :-)
Forgot to add...I contacted my water people (Cobb County, in Georgia) by calling the customer service line and what I got was this:
"Hi, is this the Cobb County Water customer service line?"
Click (person hung up phone). :shock: ?????
Sooooo....getting info from them on changes in pH at the municipal level might not be so easy...:-?
Also I forgot to add the second reason for being concerned, or rather disappointed, in my sudden increase in pH is that there is less dissolved CO2 in my water now and I worry about how that will affect my plants. For the tanks's young life (2 months) I've so far not had an algae problem - with my DIY CO2 generator and 2x/week dosing of Flourish (lighting on this 43gal, 24" high tank is 1 25W Life-Glo T8 and 1 30W 10,000K light, on for 10hrs/day for the past 3 wks, up from 8hrs/day). I concerned that the pH fluctuation might distrupt a delicate balance...what do you think?
I've never used CO2 so I have no experience in its effects under pH changes. The pH of the tap water may tell us a lot, or suggest probabilities anyway. Personally, given your fish requirements, I would be inclined to not attempt raising GH or KH, but here again the pH of the tap water is crucial to determining this necessity. I messed around a bit with mine last October/November, in hindsight it was rather foolish, as I set my plants back a good deal with the increased minerals and it took several months to get them back in shape.
We will continue to find the cause of the rise in pH, but at least it is not fluctuating back and forth, and this is good. While the fish can usually tolerate a change with little or no harm, fluctuating pH is a different matter.
OK....so...took samples of both tap water and aquarium water and left them out in a open test tube overnight. Here are the results (drumroll please... :lol:)
Aquarium water pH: 7.4
Tap water pH: 8.0
:shock: What the heck do I make of that???? My tap water has never, ever been that hard that I know of. When I kept my old tank, the water was consistently 7.0-7.2 , depending on whether I let it sit overnight or not. Soooo...I guess the change has to do with my municipality bumping the pH up by 1.0, which made my tank water pH raise by 1.0 as well.
But I have a question: why is my tank water 7.4 this morning? This surprised me a little bit.
Oh, and gH and kH of the tank water were 3 last night, nitrates 10ppm (a little high for this tank; usual reading is 5ppm). Ammonia and nitrate both 0. I wish I had thought to check the gH and kH of the tap water as well. Maybe I'll have my husband set out a glass of water so I can check them when I get home this evening.
What are your thoughts, Byron? And if the municipality is adding things to raise the water pH, what are they adding and will it negatively effect my plants/fish???? :-(
First on the tap water, contact the water people (they may have a website with this info, otherwise call or email them) and find out exactly what they are adding; explain you have tropical fish and need to know in order to properly do what has to be done. I have this issue here; our water comes from a mountain reservoir and has no hardness (near zero) and a natural pH below 6. In 2001 they decided to raise the pH for domestic reasons, and in response to my enquiry they have explained that they add soda ash (or something like that, going from memory) to raise it to 7.0 or 7.2. This has no effect on fish or hardness, so it makes no difference and I have managed fine for the past 9 years since they initiated this. But various substances vary, so you need to find out what. Find out the specific hardness at the same time. And anything else. Nitrates might be in the water too. One should always check ammonia, nitrite and nitrate in tap water initially to know what to expect; and periodically if there is reason to suspect changes.
As for the tank, with such low hardness, pH will drop in an established aquarium as I explained previously. If you did no water changes at all, it would be back down to your 6.2 within no time [of course, depending upon what is going in the water to raise it]. So, changing less water at a time will keep it from fluctuating back and forth so much, and work to stabilize it. When I do my 50% water changes, the pH in the tanks rises from say 6.2 to 6.6, then over a day or so falls back. This is harmless to the fish and plants, as it is no different than the daily diurnal fluctuation. But if I had tap water at pH 8 I would change less water and perhaps twice a week instead of once, to ensure less fluctuation. But once again, it depends on what they are putting in the water to raise it.
What a great explanation and suggestions...thanks so much. I'll try calling the water people again (they seem to have no email...they make it quite difficult to contact them) and try to get answers to what is added to the water, as well as hardness and nitrates (I have been wanting to know that actually...I think it might be around 5 ppm because that's what it is in my tank and I have a very low bioload).
Thanks so much for your help!!!!
Sorry I didn't have time to read all of the posts, but I just wanted to say that I had a similiar problem.
I talked to a chemist friend, and they told me about how acids and alkali can be 'weak' or 'strong', which has nothing to do with the actual PH of the acid or alkali, it describes how strong the bond is between the parts of the molecules...
Sodium Bicarbonate has a ph of around 8, but it's a "soft" buffer- After the bacteria in the water get hold of it, they break the bonds that hold it together, and (forgot the details) bond together in another form, becoming a 'strong' acid.
It explained why I add baking soda, ph rises, and in a couple days the ph is back to what it was... And takes even more soda to raise it again.
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