Any Chemists want to comment on PH, GH and KH - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 5 Old 11-22-2012, 11:43 PM Thread Starter
TitanTDH's Avatar
Any Chemists want to comment on PH, GH and KH

Ok, have been testing my water and getting varied results especially with PH. Currently reading the following.
A 0ppm
NO2 0ppm
NO3 20ppm
PH 7.4
KH 2
GH 9

I have noticed that the PH is fluctuating from 7.0 to 7.5 and reading a few other posts have come to the conclusion that the KH is the problem, and Extreme PH swings are bad. Now the big issue is i want to stabalise my PH at around 6.8 (Tap water is usually very constant at PH 7.2 KH 2.0 and GH 10). This is purely in the interest of me learning so i just wanted to get some advice before i put the mad scientist hat on.

I have read that peat moss will lower the PH in the tank. Given my low KH should i use Bicarbonate soda to lift the number up to around 5 or should i use the peat moss first and lower it. Then stabalise the tank with Bicarbonate soda

A further foot note is i plan to pre condition my 25% WC water with peat moss and Prime at least 1 week before changes to remove any potential swings and stabalise the PH. Once i figure it out.

The tank holds 9-10 US gallons
Live Planted
And 6 months old.

Any help is alway appreciated
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post #2 of 5 Old 11-23-2012, 06:00 AM
Geomancer's Avatar
Whatever you do, don't add baking soda. You can read up about how all this works here:

Do you shake the tap water really well, or let it sit for a full day before testing it? The pH can often rise.

However, the pH of a tank should never rise above the tap water ... unless you have something in the tank causing that to happen. A calcareous substrate (say crushed coral sand) or rocks (like limestone), decoration, something.

In a normal tank, especially one with a low KH, the pH should actually fall over time. I'm assuming your numbers for GH and KH are in degrees and not ppm?

Do you test the pH at the same time every day? A tanks pH will naturally change throughout the day, one reason is CO2 builds up during the night when the plants are not using it, and CO2 lowers pH.
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post #3 of 5 Old 11-23-2012, 08:54 AM
I'm not a chemists but can I respond anysay?

PH is a function (among other things) of carbon dioxide. In ponda, lagoons and so on that pH fluxuation you measured it entirely normal due to plant/algae action and changes in carbon dioxide levels. Light on less carbon dioxide, higher pH. Lights off more carbon dioxde pH lower.

So to me the real question is not the pH fluxuation or levels but rather the underlying cause.

If all that is happening is the pH drops down at night due to plant action that is not something to worry about. Because the ph drop is probably from a much higher lights on ph due to plant action so that the average daly pH is much higher then if no plant action was happening. Hence that tank actually has much higher pH levels vrs a tank with no plants. Therefore the carbon dioxide from the fish is being totally consumed resulting is low carbon dioxide and high oxygen levels. Hardly a bad environment for the livestock.

So when I measure pH, I always measure it just before lights out each day. If that value is high, I don't worry.

my .02

maintain Fw and marine system with a strong emphasis on balanced, stabilized system that as much as possible are self substaning.

have maintained FW systems for up to 9 years with descendants from original fish and marine aquariums for up to 8 years.

With no water changes, untreated tap water, inexpensive lighting by first starting the tank with live plants (FW) or macro algae( marine)

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post #4 of 5 Old 11-23-2012, 10:05 AM
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post #5 of 5 Old 11-23-2012, 11:56 AM
Byron's Avatar
I agree with beaslbob that the fluctuation is probably the normal diurnal cycle, depending when you are testing, and this is not a problem. It occurs in most natural waters and fish are used to it. Always measure the pH the same time each day in order to get a clearer idea of any fluctuations aside from the afore-mentioned. And try to do it in daylight as the colours will be more reliable; all artificial light sources can distort them.

The article Geomancer linked is my summation of the issue [and Reefing's linked article is one of the sources I used] and as it notes therein, diluting the water is the safest method. Any additives will carry risks, depending.

Each tank is biologically unique however. I have 7 tanks running, all receiving 50% water changes weekly with tap water that is near-zero KH and GH and a pH of 7. Plant fertilization including a GH booster (Equilibrium) is identical in all tanks. Yet some remain at pH 6.4-6.6, one or two at 6.8, and one at 7.2. And these are very stable, according to periodic tests carried out prior to the water change in early morning, and over a period of months.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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