Why do you need to test both the dH and the pH?

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Nicki Gaga

Aquarium Advice Freak
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Jul 17, 2014
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If they both tell you the acidity or alkalinity of the water , what's the point of knowing both? And why are there tests for each?
 
Did you mean KH and/or GH? Those test the hardness of your water, not the pH. While they are related to each other, they're not the same thing.


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I've never bred fish (on purpose).
The water's Hardness is basically the water's mineral content. The more minerals, the more difficult it is to alter the pH. The fewer minerals, the more likely you are to have swings in the pH level. An unstable pH is bad for fish whether or not you're trying to breed them.


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KH is the carbonate content of the water, which is the buffering capacity. Low KH water can be subject to pH swings. (Incidentally, I have low-KH water and my pH never seems to deviate from 7.4.)

GH is the "hardness" of the water, or the water's mineral content.

pH is a logarithmic scale of the hydrogen ion concentration in the water.

They're all important, though GH and pH are most important. Fish that naturally live in soft water strongly prefer low-GH water. Fish that live in hard or brackish water strongly prefer high GH water. Some fish can be acclimated to living in tanks where the pH is a lot different from their natural habitat (especially if they're raised in neutral water). Fish are less adaptable when it comes to living in conditions where the GH is radically different from that of their natural habitat.

You should purchase kits for and test your tank's pH, GH, and KH before stocking with fish. Knowing your pH and GH will give you an idea of which species will tolerate your tap water without modification. If you want to keep fish that live outside of your tap water's chemistry, you'll have to make adjustments. If your KH is super-low, you may want to add baking soda to give your tank water better buffering capacity.
 
But if I test the pH, wouldn't that test the gH too because if the pH is low, does it also mean the gH is low too?
 
Testing the Tank Water

If they both tell you the acidity or alkalinity of the water , what's the point of knowing both? And why are there tests for each?

Hello Nick...

The only water testing needed is during the nitrogen cycle. Once the bacteria colony is established, the tank is cycled. From this point on, you remove half the tank water or more weekly and replace it with pure, treated tap water. No testing is really needed, because the toxins are always removed through the weekly water change. The water chemistry is always stable.

B
 
But if I test the pH, wouldn't that test the gH too because if the pH is low, does it also mean the gH is low too?

There is typically a relationship between Hardness and pH. Hard water results in high pH and soft water usually means low pH... usually, but not always. When you're testing your waters hardness, what you're actually checking is the water's pH stability... or how likely it is to change. A pH that suddenly raises or drops is not healthy for your fish. Knowing the water's hardness allows you to be prepared for such things.
Here's a fun fact though: Nobody's forcing you to do this. You asked if GH and pH were the same thing. They are not. Question answered. Now that you (hopefully) have a better understanding of what they are and how they relate to keeping fish, you can decide for yourself if you want to test either, both or neither.

BBradbury: Not helpful. If you don't know the answer to somebody's post, then feel free to not reply. In this case, the OP asked what, if any, difference there was between GH and pH. Your answer was to tell him to do large, weekly water changes (your favorite thing to Copy and Paste it seems). Not really sure what the removal of nitrate has to do with pH and GH.
 
Tank Chemsitry

There is typically a relationship between Hardness and pH. Hard water results in high pH and soft water usually means low pH... usually, but not always. When you're testing your waters hardness, what you're actually checking is the water's pH stability... or how likely it is to change. A pH that suddenly raises or drops is not healthy for your fish. Knowing the water's hardness allows you to be prepared for such things.
Here's a fun fact though: Nobody's forcing you to do this. You asked if GH and pH were the same thing. They are not. Question answered. Now that you (hopefully) have a better understanding of what they are and how they relate to keeping fish, you can decide for yourself if you want to test either, both or neither.

BBradbury: Not helpful. If you don't know the answer to somebody's post, then feel free to not reply. In this case, the OP asked what, if any, difference there was between GH and pH. Your answer was to tell him to do large, weekly water changes (your favorite thing to Copy and Paste it seems). Not really sure what the removal of nitrate has to do with pH and GH.

Hello Coy...

The question as I understood it was, "Why do you need to test the pH of the tank water?" My answer was: "You only need to test the tank water during the cycling process." In other words, it's unnecessary any other time, provided you're a good water changer. Water changes done often enough are the key to a healthy tank. Can't preach this enough.

I think my answer was "spot on". Apologies if it wasn't up to your standards.

B
 
But if I test the pH, wouldn't that test the gH too because if the pH is low, does it also mean the gH is low too?

While low pH is often associated with soft water in nature (and vice-versa), they will not necessarily be connected in your aquarium. This is especially the case if you municipality chemically treats your water.

Hello Nick...

The only water testing needed is during the nitrogen cycle. Once the bacteria colony is established, the tank is cycled. From this point on, you remove half the tank water or more weekly and replace it with pure, treated tap water. No testing is really needed, because the toxins are always removed through the weekly water change. The water chemistry is always stable.

B

I disagree. You need to know the GH of your water before you select the species of fish for you aquarium. One should also test the tap water for nitrates, especially if you have well water in an agricultural area (where the nitrate level can exceed EPA limits). It is also helpful (though less critical) to know the buffering capacity (KH) of your tap water.

After cycling and while slowly (over a period of weeks) stocking your tank, it's also helpful to check the pH, ammonia, and nitrite levels every few days to ensure that your newly-established bacterial colony can handle the tank's bioload. Over this time, it's also helpful to do weekly nitrate tests, to ensure that the tank's nitrate concentration is low enough to be healthy for your tank's species (this is especially critical when you have sensitive fish, like rams).

The water chemistry is not "always stable." Wells sometimes get contaminated by runoff or experience bacterial outbreaks. Even municipally-treated water systems occasionally experience variability in water quality. While one should not *expect* these things to occur, it's still a good idea to test an established aquarium's pH, ammonia, nitrites, and nitrates once a month or so.
 
+1 to the above. Water sources vary from place to place and there exists the possibility for it to change over time. What might be true for some people may not be the case for others. I don't personally test my GH and pH very frequently, but I did initially to get an idea of what my tap water's chemistry is and how consistent it is. Currently I only check it every 3-4 months to make sure there aren't any major shifts.

Here is the original post:
"Why do you need to test both the dH and the pH? If they both tell you the acidity or alkalinity of the water , what's the point of knowing both? And why are there tests for each?"

How you turned that into "Why do you need to test the pH of the tank water?" I do not know.
 
I'm asking what's the difference between gH and pH if both of them measures the acidity of alkalinity of the water? It's fine. Sorry for he inconvenience.
 
Hello Nick... The only water testing needed is during the nitrogen cycle. Once the bacteria colony is established, the tank is cycled. From this point on, you remove half the tank water or more weekly and replace it with pure, treated tap water. No testing is really needed, because the toxins are always removed through the weekly water change. The water chemistry is always stable. B

+1
This is all you need to know.
 
Oh sorry for the inconvenience. What I meant was what's the point of checking BOTH the gH and the pH if both of them measured the acidity of alkalinity of the water?
 
Hello Nick...

The only water testing needed is during the nitrogen cycle. Once the bacteria colony is established, the tank is cycled. From this point on, you remove half the tank water or more weekly and replace it with pure, treated tap water. No testing is really needed, because the toxins are always removed through the weekly water change. The water chemistry is always stable.

B


I strongly disagree. It's very important to test your total chemistry. I found out the hard way. You have to make sure your putting fish in that live in your water conditions. Different fish different requirements. Regular testing is a must. After awhile if your chemistry does not fluctuate then you can slack on testing.


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The fish keeping hobby does not require so much knowledge of chemistry. Most breeders I know concentrate on frequent water changes and proper feeding... Period.
On almost a daily basis I see newcomers get discouraged by being misled about their kH, Gh too hard, too soft, add this chemical and check some more, what chemistry set to own etc.
Sorry for the rant but way too much focus on silly water parameters and water chemistry.
 
The fish keeping hobby does not require so much knowledge of chemistry. Most breeders I know concentrate on frequent water changes and proper feeding... Period.
On almost a daily basis I see newcomers get discouraged by being misled about their kH, Gh too hard, too soft, add this chemical and check some more, what chemistry set to own etc.
Sorry for the rant but way too much focus on silly water parameters and water chemistry.

Except that all of those "silly water parameters and water chemistry" are important.

Internet forums such as this one are full of people wondering why their 20 Cardinal Tetras died in their tank that is pH 8.2 and 20 dGH. Or people who don't understand why their GBRs keep dying in their well water that contains 20 ppm nitrates. Or people who are on their second month of cycling, at pH 5.8 and 68 degrees F. All of those egghead parameters are important. If more people took the time to educate themselves about their meaning and put in the time/effort to ensure proper water conditions for their fish, far fewer fish would die.
 
The fish keeping hobby does not require so much knowledge of chemistry. Most breeders I know concentrate on frequent water changes and proper feeding... Period.
On almost a daily basis I see newcomers get discouraged by being misled about their kH, Gh too hard, too soft, add this chemical and check some more, what chemistry set to own etc.
Sorry for the rant but way too much focus on silly water parameters and water chemistry.


These silly water parameters keep your fish alive and healthy. If you notice I said to start off checking very regularly. If your water chemistry does not fluctuate then you can test less often but still important to test regardless.


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Except that all of those "silly water parameters and water chemistry" are important. Internet forums such as this one are full of people wondering why their 20 Cardinal Tetras died in their tank that is pH 8.2 and 20 dGH. Or people who don't understand why their GBRs keep dying in their well water that contains 20 ppm nitrates. Or people who are on their second month of cycling, at pH 5.8 and 68 degrees F. All of those egghead parameters are important. If more people took the time to educate themselves about their meaning and put in the time/effort to ensure proper water conditions for their fish, far fewer fish would die.

Internet forum like this one is full of people giving lots of good information but unfortunately some bad information as well. Most fish deaths you have described come from poor water conditions, not so much because of what comes out of the faucet but the conditions that have been created inside of the tank due to over feeding, temperature, lack of water changes and even trying to "adjust" water parameters like pH with buffers and such. Add fish waste to the mix and that confined tank is trouble brewing. I also believe that many fish are doomed from day one, not knowing it's history or where they come from, when two month later they die, we blame it on water parameters. Of course there are always extreme conditions as you have mentioned that are less than ideal.
BTW I have kept and raised most of the fish you have mentioned here for years plus discus and angels with nothing more than an ammonia tester, which has only been used when setting up a new tank.
This is a forum of opinions and to share knowledge but bottom line anyone can do what they want with their fish and if it feels good for some to spend hard earned cash on a chemistry set, by all means, my thought is that much of the basic needs of the fish and what truly makes a confined environment healthy for them has gotten lost in the mumbo jumbo of water parameter testing and other useless worries.
 
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