Before I start off, i would like to warn anybody reading this that this involves, to a degree, some involved water chemistry. By all means not advanced as i will try my best to keep it as simple as possible, while helping others understand the topic much better...

I see that there is many threads and links around that tell you what pH, kH and gH is safe for your particular fish, as well as how to increase, decrease etc. these numbers. What there is a lack of, is an understanding of these numbers, and what they have to do with you or your fish. Hopefully this will help you out and understand your fish better. After all, is that not what you want to do?  I will explain the importance of the essential minerals in your fish’s life, using the pH, KH, GH values

We've all unfortunately come across the poor guy who bought a new tank and straight off worried about pH... We've all done this. I know I did: "Bought 2 bottles of pH down and pH up. The pH was 8.2 from the tap so i put pH down and the next day it was at 7.4... GREAT!!! Next day it's back up to 8.0 so more pH down with a double dose to be sure it's safe. pH plummets to below 6.0 the next day, so pH up at half dose and the pH is at 7.2... GREAT!!! Next day it's back up at 8.0"

By the end of the day, we've spent a pocket-full, got no results, broken any chance of a cycle having the possibility to start, have a handful of dead fish, very milky water and some staining of everything in the tank. So there we are with less money, less fish, less chemicals and less quality in terms of water. I believe that these chemicals can be used safely in the home aquarium without these hassles, but if you do not understand what it is, or how it works, then unfortunately you will end up with a tank like my first one!  Nobody wants that. Nevertheless, this can and unfortunately will get tricky, but here goes... ... ...

When it comes to water chemistry in aquariums, there are two big sections to consider. These are Water Parameters and Water Quality.

Water Quality is defined by how safe your water is for fish. These are things like Ammonia/Ammonium, Nitrite and Nitrates. The less of these, the higher the water quality is essence. That's quite simple right, yes right...

Water Parameters is defined by a reading of a specific "thing" of your water. Naturally, these do not affect water quality direcly, but are just as important to good fish health. These are things like temperature, pH, KH, GH, conductivity, viscosity, volatility... believe me, and the list will never end. The ones we will focus on, because they are mostly relevant to our aquariums, are:

1) pH (also known as per Hydrion or percentage hydrogen)
2) KH (also known as Carbonate Hardness)
3) GH (also known as General Hardness)
4) Temperature (not also known as)
5) How to safely adjust these values

Now, Fish have a specific bodily function which we call Osmoregulation, which in simple terms is the fish's function that regulates it’s intake and expulsion (balancing) of minerals and water throughout its body. A healthy osmoregualtion system goes like this: Water goes in through the mouth, out the gills, out the skin and excreted; this is then replaced by minerals taken into the skin, or “drank” through the gills so to speak, and vice versa. Without this system a fish would either suffer from lack of the correct balance of minerals, or too much of one mineral, resulting in some form of deficiency. This is often what is believed to lead to the disease of fish not properly acclimated, which is why the “floating bag” method is so widely discouraged by the more experienced nowadays Fish osmoregulation is needed by fish because although we as humans get all our nutrients and minerals through food, fish live in an environment where these are readily available to them, which is why the correct balance of your water parameters is so important to your particular fish.
Note: freshwater fish and saltwater fish systems work on a different level and are not the same. The basics however, as I will explain further, are the same.

1) pH - per Hydrion... "I've never heard of that" Well here's your lesson. Per Hydrion refers to the amount of hydrogen, in its ionic form "Hydrion", that is in a solution, in our case, tank water. The pH scale is a logarithmic scale, and therefore means that 6.0 pH is 10 times more acidic than 7.0 pH, and 5.0 pH is 100 times more acidic than 7.0 pH . Now to understand how hydrogen changes pH, we need to understand what makes your water acidic (below 7.0 pH) or basic (above 7.0 pH). "H+" ions make water acidic; "OH-" ions make water basic. You may notice that with those two together, there are two hydrogen atoms, and one oxygen - yeah that’s right... Water, H2O. That is why pure water is the most neutral substance in existence, exactly 7.0 pH... The unfortunate fact is that pH in aquariums isn't stable without other minerals as I mentioned above, such as calcium, magnesium, Sodium, Iodine, Chloride, etc etc... These are what KH and GH measures are partly for.

So how does any of this help my fish? Well that's where the other parameter's come in. But before we go into the heavy detail stuff, i would like to mention this:

- Besides very specific fish, such as African cichlids, most fish will live HAPPILY in water that has a pH of between 6.6 and 8.2. Fish are very adaptable creatures, and as such can easily adapt to these conditions. The most important factor to keep in mind is, even at the very extremes of the pH scale, it is more important to keep the pH constant than at a precise value.

2) KH – Carbonate Hardness... The reason this is called carbonate hardness is because it measures the amount of Calcium Carbonate (CaCO3) that exists within your water. Again, in a very complicated way, this is what prevents your pH from having the ability to “crash” or even budge. If you are aiming to lower your pH, you need to lower this value in order to do it. Calcium is the most abundant mineral within water, and is especially important in the lives of marine, brackish, or even rift lake fish. A fish that has a “hard water” or “soft water” requirement to keep, simply means that that fish has evolved/adapted it’s osomregulation pattern over many generations to take up a certain amount of minerals from the water in a given time, which is categorized by whatever body of water that fish has lived in...
Hard water fish – take more minerals up in a given time
Soft water Fish – take less minerals up in the same given time
That would then very simply explain why soft water fish are easier to adjust to hard water than it is to do the reverse. Soft water fish are able to still take up minerals in the water because there is an abundance of it in hard water, whereas hard water fish struggle because they need to take up minerals, which simply aren’t there in soft water. This is not to say that soft water fish can live fully comfortable in a hard water environment, because hard water tanks have a higher pH than soft water tanks, and the same for the reverse situation This is the one of two (but not only 2) prime reason why it is important to know your KH value in your aquarium. Calcium therefore plays an important role in the tank in that 1, it stabilizes the pH (but also raises it) and 2, it plays the one of the biggest roles in fish osmoregulation.
Calcium as we all know promotes good bone growth, teeth quality... The usual. What it also serves to do however, is regulate blood flow, helps immune system functions, aids in metabolism and is required in its free ionic form for necessary and quality heart function. Think it’s important yet?
Now you may ask, but why does calcium carbonate make my water more basic? Well, good question. The Calcium carbonate is broken up in water into Calcium (Ca) and Carbonate (CO3). Carbonate is extremely unstable so it will match up with “H+” ions. Remember now that these make your water acidic, but because there are now less of them, it will make your water basic.
So as you can see, KH is a very important value in your aquarium, even more important than pH IMO, simply because on most occasions, the value of KH is almost a direct correlation to the value of your pH.

3) GH – General Hardness ... Luckily for us, we have a measure that can tell us the amount of all the minerals dissolved in our water! While Calcium is important, without other minerals that the GH value measures, it is useless, some even claim it is more dangerous as such. Your GH test kit measures the amount of all minerals in our water, including, but not only Carbonate Hardness like KH. This is also helpful as water does not only have calcium for fish. These other minerals (at least the most important ones) are:
- Magnesium (Mg)
- Chloride (Cl) (NOTE: NOT chlorine (Cl2))
- Sodium (Na)
- Sulphur (S)
- Potassium (K)
Beyond these there are many others, but are not really measurable without extensive testing. The main reason GH is also important in home aquaria, is because it measures the very important Magnesium. Magnesium performs the same ideal function as Calcium. Fish need it for osmoregualtion, just as they need Calcium. Magnesium serves to aid in digestion, improves immunity, aids in growth (of both bones and muscles) and development of the gills. See why this is also important? I sure do!...
Magnesium therefore is also important to your fish’s development, just as is Calcium, and the other minerals. This is why there are also other water parameters to consider rather than just temperature and pH. There are many things that will change your pH, such as Ammonia, Nitrite and Nitrate – hence why many say that it is pointless to test pH during a cycle.

4) Temperature – Boy this is a tough one... After all your study on pH, KH, GH, electrolytes, minerals, fish function... Now you have to deal with this... Okay so here goes. Temperature – Keep it constant... Wow okay glad thats done... moving on now...

5) How To Safely Adjust These Values – Nowadays, it is easy to access equipment or supplies that will aid in adjusting pH, KH and GH (and temperature – new tech called a heater )

- How to raise pH – In order to raise your pH, you must increase your kH value, and preferably your GH value as well. Remember how I said that in most cases your pH value is a direct correlation of your kH value? Well yes, your kH or buffering capacity will increase your pH as it increases itself. The following methods can be used:

1) Aquarium Buffer – Whether bought or home-made, make absolutely sure you do your research here. This can cause many issues if not played well, but if executed correctly can be a great pH buffer (by adding minerals to your water thereby increasing your kH and GH values). If you do not have a full understanding of redox potentials/electrolysis in aquariums then I urge you not to try homemade mixes.

2) Aragonite/Crushed coral Substrate – This is commonly used in hard water aquariums because the substrate leaches minerals into the water. I note that these do not leach all the minerals required but do serve as a good starting point to raising pH correctly.

3) Crushed Coral Filter – This is helpful when combined with method #2, because the combination provides all necessary minerals for FULL healthy osmoregulation of hard water fish. The crushed coral leaches predominantly calcium into the water, but also other trace elements.

4) Addition of Aquarium Salt – This is dependent on what salt we are referring to here. Marine Salt mix, yes, it is a great source of the necessary nutrients in hard water, but be careful on the dosage. You are aiming to add minerals to the tank, not overdose it. Regular aquarium salt is a no, no. Good treatment in diseases yes, terrible aid in raising pH safely.

- How to lower pH – In order to lower your pH, you must decrease your KH value, and again, preferably GH too. Be careful though. It is safer to keep a soft water fish in slightly harder water than to keep a soft water fish in a very soft water environment. The reason being: Harder water holds its pH value much better than soft water. pH crashes and inconsistent pH values can be attributed to KH every time. Not sometimes, EVERY TIME. Note that you will not be able to lower your pH without lowering your carbonate harness.

1) Aquarium Buffer – Same as above, research is essential. I suggest using the buffer to lower KH and thereby lower pH, and combine this with a tiny amount of shell in your tank, or small amount of crushed coral in your filter to simultaneously buffer the water, which means that your pH will remain lower, but relatively stable because of the buffer being released by said shell or coral. Homemade mixes include potassium salts. Stray away from these as they will only temporarily lower your pH, then “jumping” it back up which will be more stressful to the fish in any case.

2) Carbon Dioxide Dosing – Carbon Dioxide serves to lower your pH and is a great plant nutrient. 30 PPM of CO2 will lower your pH by 1 degree - I.e. from 7.0 ph to 6.0 pH. Be careful of homemade mixes as the CO2 isn’t constant and can therefore play with your pH, resulting in stressed out fish.

3) Peat/Clay Substrate – This will leach minerals into the water that will bond with the Carbonate thereby preventing it from bonding to the “H+” ion we discussed much earlier, thereby lowering KH and subsequently pH. This is a good method for planted tanks as the nutrients can also be used by plants.

4) Peat Filter – Same as the substrate version pretty much, just that it has a higher flow through it and therefore leaches faster. Be careful not to use too much.

5) reverse osmosis / De-Ionized Water - This method is commonly used because RO/DI water has effectively 0 Hardness (both KH and GH). When mixing this with other water, it can have an overall "softening effect" and thereby lower you pH safely. Be sure not to use too much RO/DI water as you still want some value to water hardness (again both KH and GH) in your tank. Distilled Water can also be used as above.

Lastly, I note that it is important to buffer your water very slightly while trying to lower it. This will allow your KH levels to drop but not to plummet, and thereby keeping you pH relatively constant, even in a soft water aquarium

It is however, important to note that pH is EQUALLY important compared to KH and GH. I am not aiming to promote that you forget about pH entirely, but to consider why your pH is where it is, or why there are problems etc. Remember, a fish that lives in 8.0 pH waters will not do well in 9.0 pH... Remember why? No? Don’t forget that 9.0 pH is 10 times more basic than 8.0, so it isn’t just a “1 point pH jump”, it’s a big change to have. Imagine you living in 60 degrees your entire life, and then over the time of 2 hours adjusting to living in 600 degrees (it is 10 times extreme afterall?).

This is to serve an even further purpose as to why minerals (especially calcium and magnesium) are so important in your fish’s lifetime and why it is so important to keep your pH stable, and guess what? You can provide your fish with the necessary minerals while doing it!

I hope that you, reader, have found this interesting at the least if not useful. Good luck and happy fish keeping!
Please if you have any questions or queries do not be afraid to ask. If you have anything to add to this, please do speak up and I will be happy to include it!

Acknowledgments

Thanks to my friend Josh McDonald for all his help in writing this article.