Using De-ionized Water to Lower pH

[Sam Sheridan]

Hello,

I've been looking into keeping Apistogrammas however my local tap water has a high pH and is relatively hard. I understand Apistos prefer softer, acidic water so thought that I could achieve this by mixing my tap water and de-ionized water in a set ratio to reach a desired pH.

I take A level chemistry and calculated that in my 8.5 litre water change I would need 7 litres of tap water (pH 7.8) and 1.5 litres of de-ionized water (pH 6.4). I tried to do this today for my first water change however after testing the pH of the water I was about to put in the pH came out as 7.8 still.

I use test strips which I know can be inaccurate so thought that this may be the reason for the high pH. I have also read somewhere that hard, alkaline water contains buffers which resist changes in pH, is this true? If so, what method would you recommend to lower the pH and soften my water? I don't particularly want to invest in an RO unit, as I currently don't have the time or money to arrange that.

Thank you for any help!

- Sam

 

[StevenF]

Potassium and sodium hydroxides and carbonates in the water are the most common causes elevated PH. They are highly water soluble and can easily push the pH to 10 or higher Hard water also contains calcium and magnesium carbonates are also in the water. These can also push PH up but there solubility is PH sensitive. As a result they will push the PH up to a maximum of about 7.

The only way to reduce the PH is to reduce the amount of K, Na, Ca, Mg in the water. using RO or DI water. It is always best to have a mix of RO / DI water and tap water. Using pure RO and DI water requires the water to be remineralized before adding it to the tank which much can make it harder to reach a specific PH and grow plants.

I am not familiar with this fish but according to a web search I did it requires a 30 gallon tank minimum. Most people do between 30% to 50% water change once a week to maintain stable mineral levels in the water. If you have an appropriately sized tank (30 gallons) you are going to need a lot more than 8.5 liters for a water change.

 

[Sam Sheridan]

Thank you for your response!

The Apistogramma I'm looking to buy is an Apistogramma agassizii which are small and can be kept in 15 gallon tanks (which is what I have).

My original plan was to use a mix of de-ionized water and tap water which hasn't seemed to work as the pH stayed the same as the tap water. Would using RO / DI water and tap water be different?

 

[hobby5]

@StevenF
I am very sorry to say that, but you should take some chemistry classes. I think I corrected you before, but you still spread this false information.

K, Na, Ca, Mg ions in the water DO NOT influence the pH in a significant way. The main factor is KH, which is the concentration of carbonate, which is also the buffering agent in the water.

@Sam Sheridan
pH is not the most important number when keeping soft water fish. More important are KH, GH and TDS. If those are in the right range pH will in most cases be right too. With a low KH you could decrease pH further using alder cones or leaves (almond, oak, or some others).

I don't know what kind of calculation you did but without knowing the buffering capacity of your water it is impossible to calculate the pH of a mix. Practically, RO and DI water are the same. But to know how much you need, you will have to determine KH of your tank and tap water first.

The aquarium strains of Apistogramma agassizii don't require extreme values. KH of 2-3 °dH and pH around or slightly below 7 should be fine. Also your tank size should be sufficient for a pair if it is well structured and has enough hiding places and caves.

 

[Sam Sheridan]

Thank you very much that all makes a lot sense. The calculation I did assumed that hydrogen ions were the only thing affecting pH which I now know is definitely not the case and explains why my pH wouldn't budge.

My KH is 6 and GH is 8, would you happen to know a rough ratio for tap : de-ionized water so that a pH of around 7 could be achieved?

I've heard about using leaves to soften water and lower pH but wasn't sure if this was a good idea, as when tap water is put in after a water change wouldn't the hardness rise again and take time to decrease? I thought keeping a steady hardness and pH would be better.

 

[hobby5]

There are many different online calculators out there. Here is one:
http://linuxhost.matsp.co.uk/calculator/ph-from-kh.php?KH=36&CO2=5

Let's assume you aim for a KH of 2 °dH. So your ratio should be 1:2 for tap : de-ionized water.

And you have to keep that ratio with every water change. So in the long run it is better to get an own RO system.

An ideal Apistogramma tank would have a thick layer of dead leaves on the ground. On the surface of those a rich flora of infusoria will develop. Which will be a valuable food for eventual fry and also the adult fish will feed on this.

Don't worry about the pH changes during water changes. If you add water with the same KH, those will be minor.

 

[Sam Sheridan]

Thank you for your help. It certainly might be with investing in an RO system in that case!

One last question, do you happen to know how water that is passed through my house's water softener will affect this? I've heard it can be bad as sodium ends up in the water but could it be worth using it?

 

[hobby5]

Most people consider water originating from a water softener not suitable for fish. I follow this believe, but haven't seen a thorough explanation for it, yet. (If anyone can point me to some I would be very happy.)

The water softener removes the magnesium and calcium ions and replaces them with sodium ions. So the problem could be too much sodium or not enough calcium and magnesium for the fish.

But you can use that water for your RO system without problems.

 

[Sam Sheridan]

That makes sense, thank you for the advice.

I may go for one of the more forgiving species of Apisto like borellii or cacatuoides in that case.

 

[Byron]

Most people consider water originating from a water softener not suitable for fish. I follow this believe, but haven't seen a thorough explanation for it, yet. (If anyone can point me to some I would be very happy.)

The water softener removes the magnesium and calcium ions and replaces them with sodium ions. So the problem could be too much sodium or not enough calcium and magnesium for the fish.

But you can use that water for your RO system without problems.

Water Softeners [cited verbatim from Dr. Neale Monks, Wet Web Media]


“Domestic water softeners do not produce soft water in the sense that aquarists mean. What domestic water softeners do is remove the temporary hardness (such as carbonates) that potentially furs up pipes and heaters by replacing it with permanent hardness (such as chlorides) that does not. While you can pass this softened water through a reverse-osmosis filter to remove the permanent hardness as well, until you have done so, you shouldn't consider the softened water as being suitable for soft water fish.

In fact, aquarists are divided on whether the resulting softened water is safe for keeping fish at all. The odd balance of minerals in softened water is not typical of any of the environments from which tropical fish are collected. While the chloride levels are much higher than those soft water fish are adapted to, the levels of carbonate hardness are too low for the health of hard water fishes like Rift Valley cichlids, goldfish, and livebearers. So the safe approach is not to use it in any aquarium, and instead draw water from the unsoftened drinking water source in the kitchen.”

 

[Sam Sheridan]

@Byron Very interesting stuff, thank you. Would you happen to know if a dechlorinator would remove the chloride ions?

 

[Byron]

@Byron Very interesting stuff, thank you. Would you happen to know if a dechlorinator would remove the chloride ions?

I am not sure just what "chloride ions" may be, even having looked it up. Sodium chloride, which is common table salt or sea salt, is the issue with softeners. Sodium chloride is harmful to soft water fish, and many hard water species too. This is what you must avoid with sodium softeners. Dechlorinator (water conditioner) will most assuredly not remove salt (sodium chorlide).

 

[StevenF]

K, Na, Ca, Mg ions in the water DO NOT influence the pH in a significant way.

That is an extreme simplification of what is going on. The following affect PH very strongly:

NaOH
KOH
CaOH
MGOH

These hydroxides will not register in a KH test have a very strong effect on PH. but they are also less stable They can easily push the PH up to 14. It is not possible to exceed a PH of 14.

N 24 hours the above compounds will react with other compound in the water. Some of the first formed are carbonates:
Ca(CO3)2
MG(CO3)2
Na(CO3)
K(CO3)
These carbonates also effect on PH . Potassium(K) and sodium (Na) carbonates are highly soluble and will have a moderately strong PH affect. Calcium (Ca) and magnesium (Mg) carbonates can only put the PH up to about 7. They cannot push it higher. Calcium and magnesium carbonates have the least effect on PH. All carbonates are detected in a KH test.

Over days all of the above will be completely absorbed by plants or are converted to Na, K, CA, Mg nitrates, chlorides, phosphates, and sulfides:

This all have no effect on PH and will not be detected by KH test. However when the aquarium lights come on and plant growth restarts these nitrate, chlorides, and sulfates will be absorbed and or are converted to hydroxides and carbonates and PH will go up and potentially the PH can exceed 9 However once the lights go off carbonates are formed and PH drops and KH increases.

Note most people don't have lights bright enough and or plant growth fast enough to see daily PH changes. I Have however seen it and my PH was at least 9 when the lights turned off.By the next morning PH was down to between 6 and 6.5. I solved the problem by dimming my lights.

Note some people believe KH will measure carbon dioxide. It doesn't. Distilled water staturated with CO2 will have a KH value of zero.

 

[Essjay]

@Byron Very interesting stuff, thank you. Would you happen to know if a dechlorinator would remove the chloride ions?

I am not sure just what "chloride ions" may be, even having looked it up. Sodium chloride, which is common table salt or sea salt, is the issue with softeners. Sodium chloride is harmful to soft water fish, and many hard water species too. This is what you must avoid with sodium softeners. Dechlorinator (water conditioner) will most assuredly not remove salt (sodium chorlide).

Chlorine is a gas, Cl2, which can dissolve in water. Chloride is the ion derived from chlorine, Cl- [sorry, I don't know how to use superscript and subscript in the reply box to make the forumlae look right ]

Dechlorinator is a solution of thiosulphate. This reacts with chlorine, turning it into chloride. So no, dechlorinator doesn't remove chloride as it only reacts with chlorine.

And the amount of chloride makes is very small and doesn't have an impact on the fish.

 

[hobby5]

That is an extreme simplification of what is going on.

No it is not.

All the salts you mention will exist in water as two independent (!) ions, cation (the positively charged metal-ions) and anion (negatively charged, e.g. hydroxide, carbonate, sulphate, nitrate, chlorid etc.).
The metal ions have no influence on pH. If you measure for instance calcium only, you will have no idea if it belongs to the neutral calciumchlorid or the very basic CaOH. But again this is irrelevant as those cations are import for your plants and fish, but don't influence pH. Uptake of cations by plants doesn't affect pH either. The pH swing you mentioned is due to changes in CO2 levels.