Ph Mystery

[LetsBeFriends]

So for a while now I have had a bit of a issue in my 3 tanks with the ph being very high (around 8.4) and have not been able to locate the source of the problem, first i will outline the specs for each tank and then outline what i have done to figure the out the problem.

75 us Gal (2 years old)
Runs 2 filters, 1 aquaclear 110 that has biofoam and bio material and activated carbon that is a bit old, the other filter is a smaller tetra whisper 20 or 30 that currently is running with a bag of peat in it. It has has 1-3mm size gravel as its substrate, not planted, 15% water change every 2 weeks, currently housing 2 pictus catfish and one black banded leporinus. Ph = 8.0 Ammonia, Nitrate and Nitrite are all 0.

20 us gal (2 months old)
runs 1 marineland 200b filter with activated carbon, 1-3mm gravel substrate, 15% water change every 2 weeks, medium planted, liquid ferts once a week, currently has 1 tigerbarb(soon to go), 2 Siamese flying foxes and 1 hopallo catfish. ph = 8.4 Ammonia, Nitrate and Nitrite are all 0.

http/www.fishforums.net/index.php?/topic/315006-20-gallon-planted-journal/

10 us gal (1year old)
runs 1 tetra whisper 20 with activated carbon, 1.3mm gravel substrate, 15% water change every 2 weeks, lightly planted, has 6 cherry barbs. ph = 8.4 Ammonia, Nitrate and Nitrite are all 0.



Now here is the weird part, each tank is very different in style, stocking, and size, and the water that goes into the tanks is a ph of 7.2(i tested each tap in my house 3 times). I tried adding peat to the 75 gal, and it did help a bit, but i still cannot pinpoint the cause of the high ph, the rocks you see in the 75 gal have been in there for the life of the tank so i cant imagine that they are the cause especially since the other tanks have high ph as well. I even tested water that has been treated with stress coat just to make sure that stress coat was not the cause of it. the picture below is a picture of a high range ph test with the 75 gal on the left and the tap water on the right. The tap water in my house does run through a salt water softener before it reaches the taps however according to my lfs testing its still a bit on the hard side (10ish degress of hardness).

i know high ph is not the worst problem in the world but i would still really like to to bring it down some or at least identify the cause of it, any help would be really appreciated, hopefully it is just something simple that i over looked

 

[plecostomus-mad]

certain stones and slate will cause fluctuations in ph. what rocks / stones and slate do you have in all the tanks?

 

[LetsBeFriends]

certain stones and slate will cause fluctuations in ph. what rocks / stones and slate do you have in all the tanks?

the only tank with rocks in it is the 75 us gal, and it has slate and a blue stone that i honestly dont know the exact type of, however these stones have been in the tank for about to two years now.

 

[OohFeeshy]

My first thought would be to try doing a 100% water change on the 10g (because it's easiest) and monitoring the pH change over time. It doesn't give you many clues as to the cause, but more information is always handy.

 

[steelhealr]

It's the stones. Calcium. Would be interesting if you got a calcium test kit and dH kit. I"ll bet my money on the stones, assuming that your gravel is aquarium type gravel. SH

 

[LetsBeFriends]

so then it would make sense if all the tanks had high ph if i use similar gravel types in all three right. I know the two small tanks have the same gravel, its standard black gravel i bought from my lfs, cant remember who made it but i will find out. But the big tanks, the gravel has been in there for so long would it still have an affect on the water, and if it is the gravel is there anyway to fix the it?

 

[Dan Robbins]

It sure would effect the water. If you have calcium based rocks, i.e. Limestone or derivatives, the dissosiation of the CaCO3 is under equilibrium.
I dont think it is conicidental that your pH is stuck at a 8.2. This is the maximum pH acheived by addition of Carbonate/Bicarbonate buffering in the aquarium. It is important to realise that it is not the calcium itself which is driving the increase of pH, but the carbonate group CO3--
which for reasons and conditions far to detailed for this thread, will form bicarbonates.
The addition of bicarbonates will folow this reaction.
CO2 + 2H2O -------> H30+ + HCO3-
CaCO3 + H3O+ ------> Ca++ + HCO3- + H20. As a hydrogen ion is removed in this reaction the pH of the water will increase until the concentration of OH- ions is far greater than the concentraion of the Hydrogen ions. The backwards reaction prceeds via:
HCO3- + OH- + Ca++ ------> CaCO3 + H20. Calcium Carbonate is precipitate out of solution and pH is mantained at aprox 8.2.
It is important to realise at this point hat all these reactions are reversible and an equilibrium point is acheived. If the concntration of one reactant is increased, the position of equilibrium shifts as to minimise the effects of the change.
We can see that:

CO2 + 2H2O -------> H30+ + HCO3-
If we increse the concentration of the CO2, we shift the position of equilibrium to the right. We have the liberation of H30+ or you can look at it as an Hydrogen ion (H+) and therefore the reduction in pH.




As this was posted in the scietific section i didnt know wheater you wanted the brief or long winded answer. I could go into more detail if you REALLY wanted me to.
You can either inject CO2 into the water to lower the pH or remove the rocks. its worth mentioning that few filter media products are actually CaCO3 based. Have a look what you have in there also.
Dan.

 

[LetsBeFriends]

thats exactly the answer that i was looking for, ill have to find out what my gravel is made up of, and my guess is that this type of reaction would not really be affected by 2 years, meaning that the big tank, even though the gravel is 2 years old, it is still reacting??

 

[Dan Robbins]

Correct. The bulk of limestone, argonite etc is almost entiely CaCO3. As long as its there, its still leaching carbonates and calcium ions into the water.
Regards.
Dan

 

[Dan Robbins]

One more thing - to test if your gravel does actually contain carbonate compounds, remove it and add some vinger or HCl if you can.
CaCO3 + 2H+ --------> CO2(gas) + H2O(l) + Ca++(aq)
CO2 gas is evoked which you can clearly see as tiny bubbles on the surface of the rock. If you can grind the rock you may have a more convincing obserable reaction.
Dan.

 

[OldMan47]

The fastest way that I know of to reliably test the impact of your gravel is to run a side by side test of raw tap water and tap water with some gravel in it. The raw tap water is starting, as you said at a pH of 7.2 but may well show a change over time as the gasses in it escape into the atmosphere and the water gas content reaches equilibrium. The tap water with a gravel sample will also gas off but it will do something else, it will react to whatever degree it can with your gravel. The difference in pH between the water samples after a few days is the part you can attribute to the gravel. I have had many rocks pass the acid fizz test and still affect my water more slowly. The acid test is at best a quick screening to eliminate obviously bad rocks from being considered. The water sample over a few days can be used to test the ones that pass the first test.