High pH (8.3) and low alkalinity (0 KH). I want to lower my pH, any help greatly appreciated!

[Jenny D]

So my scottish water is very soft, straight from the tap, no KH and no GH. Unfortunately, in order to save pipe corrosion, the water is treated with poly phosphates and hydroxides (I believe calcium hydroxide but may also be sodium hydroxide.) This bumps my pH to 8.3. This is uncomfortably high for my liking. Reading scottish water's acceptable parameters they are even happy to go into the 9s. So I am driving myself mad, reading forum post after post, trying to work out what is best to do. Do I start dosing with strong acids such as hydrochloric or sodium bisulphate , or do I invest in an RO system? Both have pros and cons.
I'd really appreciate some advice. I have 11 aquariums right now and at a guess I use I use 300L on water change day. I have no space to store or collect water. Adding an acid sounds easier but with no KH, how safe is that? My preferred pH would be 6.5 - 6.8. I add CO2 to 2 of my largest aquariums using 5L CO2 generators fixed inline with their cannister filters. Even with CO2 bubbling away at an uncountable rate the pH is stubbornly remaining in the 8s.
Many thanks in advance!

 

[dw1305]

Hi all,
Welcome to UKAPS, when you have time, just go through the <"linked threads"> (and links in them) and it should help. I'll split it into a couple of answers as there is quite a lot of chemistry.

So my scottish water is very soft, straight from the tap, no KH and no GH. Unfortunately, in order to save pipe corrosion, the water is treated with poly phosphates and hydroxides (I believe calcium hydroxide but may also be sodium hydroxide.)

So this is the case for all of the UK with soft tap water, pH is raised and phosphate (P) added to <"control plumbosolvency via PIMS">. Basically the phosphate compounds of lead (Pb), zinc (Zn) and copper (Cu) are <"all insoluble"> and will precipitate out of the water column.

Traditionally sodium hydroxide (NaOH) was used, it is a <"strong base"> and cheap to buy. Recently there has been an <"NaOH shortage">, so calcium hydroxide (Ca(OH)2) has been used instead.

This bumps my pH to 8.3. This is uncomfortably high for my liking.

....... We can ignore the <"sodium Na+ ion in pH terms">, but you only need a very small addition of an acid (proton donor) for the H+ ion to combine with OH- ion and be neutralised as H2O and the pH to return to pH7....

Now this is going to sound a bit funny, but I need you to just ignore the pH value for the moment and concentrate on what pH actually is, I'm not the greatest at chemistry so I'll add in @Andy Pierce and @hax47 <"who are proper scientists">.

Pure water is H2O and a very small proportion of that is comprised of ions "H+" and "OH-" <"Self-ionization of water - Wikipedia"> and there are an equal number (10^-7) of OH- and H+ (proton) ions (I'm ignoring the hydronium ion). That is why pH7 is neutral, we have 10^-7 protons.

..... Water molecules dissociate into equal amounts of H3O+ and OH−, so their concentrations are almost exactly 1.00×10−7 mol dm−3 at 25 °C and 0.1 MPa. A solution in which the H3O+ and OH− concentrations equal each other is considered a neutral solution.........

Pure water is neutral, but most water samples contain impurities. If an impurity is an acid or base, this will affect the concentrations of hydronium ion and hydroxide ion. Water samples that are exposed to air will absorb some carbon dioxide to form carbonic acid (H2CO3) and the concentration of H3O+ will increase due to the reaction H2CO3 + H2O = HCO3− + H3O+. ......

H2O is an <"amphoteric solvent"> and bases are "proton acceptors" and acids "proton donors", we've added a base (OH-) and we now have more OH- than H+ ions and the pH rises, if it rises to pH8? That means we now have 10^-8 protons.

I'll continue in a new to avoid reader (and author) fatigue.

cheers Darrel

 

[dw1305]

Hi all

So I am driving myself mad, reading forum post after post, trying to work out what is best to do.

Now for the good news really, you don't actually need to do anything drastic and you can carry on using your tap water, which is still soft and without any dKH, but possibly with a minimal amount of dGH via the added calcium (Ca++) ions. If you did what to add a bit dKH? You could use potassium bicarbonate (KHCO3) or my "weapon of choice", for those without hard alkaline tap water, - <"Oyster Shell Chick Grit">.

strong acids such as hydrochloric or sodium bisulphate

I'm not keen of <"sodium bisulphate"> ((NaHSO4)), but you could use <"hydrochloric acid (HCl)">. You would need to use it as a (very) dilute solution, because your water company has only added a small amount of NaOH and you just need to add enough H+ ions to counter the OH- ions added. You don't have any carbonate buffering, so once the pH starts changing <"it will fall very rapidly">.

I have 11 aquariums right now and at a guess I use I use 300L on water change day.

That means <"rain-water"> probably isn't a starter, but it makes HCl a more feasible option. How do you prepare your water at the moment?

Personally? I'd just ignore pH and add some <"humic and tannic compounds"> via Oak leaves, acorn cups etc. <"Ripe for Picking: a Guide to Collecting your own Bountiful Botanicals">.

If you did want to reduce the pH of the water first? You could use <"citric acid"> ((C6H8O7)) easy to obtain and a lot safer than HCl, but possibly cost prohibitive with the amount of water changed?

cheers Darrel

 

[Jenny D]

How do you prepare your water at the moment?

Thank you so very much for your reply.
It had been a while since I'd checked my water so I was assuming pH 7 or thereabouts. Therefore I was adding KHCO3 14mg/L to obtain KH of around 1. I am also adding CaSO4.2H2O and MgSO4.7H2O to get to a GH around 3.6.
I was just reading about phosphoric acid as at least that adds some phosphates too. My tap water has phosphates which I think was leading to a touch of BBA but that cleared up when I bumped up my nitrates, presumably they were out of balance.

Personally? I'd just ignore pH and add some <"humic and tannic compounds"> via Oak leaves, acorn cups etc. <"Ripe for Picking: a Guide to Collecting your own Bountiful Botanicals">.

I mixed what I call tannin tea, boiled catappa and rooibos tea and added it to my betta tanks and even dosing very heavily the pH barely budged. From memory it went from 8.3 to 8.1.

You could use <"citric acid"> ((C6H8O7)) easy to obtain and a lot safer than HCl, but possibly cost prohibitive with the amount of water changed?

I actually have a massive tub of it as I use CO2 generators so I could certainly try! I think I'll set up a few 1L jugs and experiment. My biggest fear is that the stated acceptable levels Scottish Water have published allow pH to go as high as 9.
Unfortunately I think the numbers, or rather lack of control of them, is triggering my OCD. The fish and plants look fine. I probably need to just relax..... but then I should prepare for the possible pH of 9.
I really appreciate you taking the time to write such a comprehensive response.

 

[bazz]

My biggest fear is that the stated acceptable levels Scottish Water have published allow pH to go as high as 9.

I'm no expert but I would imagine the pH isn't very stable anyway at 0 GH and especially 0 KH, wavering around 8 or 9 depending on slight additive fluctuations.
If you was ever tempted to lower it using RO at least the membrane would last a long time and you have the bonus of removing Chlorine or whatever (most anything else they may have put in there).

 

[Andy Pierce]

Now for the good news really, you don't actually need to do anything drastic and you can carry on using your tap water, which is still soft and without any dKH [emphasis added], but possibly with a minimal amount of dGH via the added calcium (Ca++) ions.

Ah, not true. Recall that KH is titratable alkalinity from any source. Usually this mostly means from bicarbonate but hydroxide (which they are adding) also counts. The added hydroxide won't stay as hydroxide once the water is exposed to atmosphere, it will convert to bicarbonate as the hydroxide neutralises the carbonic acid from the CO2 (g) <-> CO2 (aq) <-> H2CO3 <-> HCO3- + H3O+ equilibrium. The water will be soft in as much as it has low levels of divalent cations Mg++ and Ca++, but it will be alkaline and have substantial bicarbonate. You definitely do not need to add any more KH, you already have lots.

I'm not keen of <"sodium bisulphate"> ((NaHSO4)), but you could use <"hydrochloric acid (HCl)">. You would need to use it as a (very) dilute solution, because your water company has only added a small amount of NaOH and you just need to add enough H+ ions to counter the OH- ions added. You don't have any carbonate buffering, so once the pH starts changing <"it will fall very rapidly">.

HCl will work of course (that's what I do) and is more or less the reversal of what the water company did by adding NaOH. After you add the right amount of HCl and re-equilibrate with atmosphere, you wind up with low KH and a little bit of leftover salt (NaCl) from the Na the water company added and the Cl you added; the OH- they added and the H+ you added of course combine to make water H2O. This amount of salt is negligible so you don't have to worry about that.

If you did want to reduce the pH of the water first? You could use <"citric acid"> ((C6H8O7)) easy to obtain and a lot safer than HCl, but possibly cost prohibitive with the amount of water changed?

I have also done citric acid for this purpose, actually I started out with that, but I shifted to HCl because citrate is metabolisable and I believe it made my copepod population increase very dramatically. HCl is very cost effective and also conveniently comes in well-defined liquid form - I like 1N (1M) HCl as a good balance between strong enough to not need crazy large amount and not so strong that it is serious health hazard (but you still have to treat it with respect).

 

[dw1305]

Hi all,

The added hydroxide won't stay as hydroxide once the water is exposed to atmosphere, it will convert to bicarbonate as the hydroxide neutralises the carbonic acid from the CO2 (g) <-> CO2 (aq) <-> H2CO3 <-> HCO3- + H3O+ equilibrium. The water will be soft in as much as it has low levels of divalent cations Mg++ and Ca++, but it will be alkaline and have substantial bicarbonate. You definitely do not need to add any more KH, you already have lots.

I will get there. I knew a <"little learning was a dangerous thing">.

cheers Darrel

 

[dw1305]

Hi all,

It had been a while since I'd checked my water so I was assuming pH 7

The problem is that pH usually needs some interpretation, so I've got around that, to some degree, by using "electrical conductivity". It isn't perfect, but the meters are <"plug and play"> and conductivity is a linear scale. If you have less than ~100 microS conductivity (60 ppm TDS)? You can alter the pH, either down or up, with a small addition of acids or bases respectively.

or thereabouts. ........ I am also adding CaSO4.2H2O and MgSO4.7H2O to get to a GH around 3.6.

I reckon that is about right for "re-mineralisation". Have a look at @Roland 's <"Soft water tank">. I still refer people to Larry Frank's article at "the Krib" <"Water Hardness">.

Therefore I was adding KHCO3 14mg/L to obtain KH of around 1.

Recall that KH is titratable alkalinity from any source. Usually this mostly means from bicarbonate but hydroxide (which they are adding) also counts. The added hydroxide won't stay as hydroxide once the water is exposed to atmosphere, it will convert to bicarbonate as the hydroxide neutralises the carbonic acid from the CO2 (g) <-> CO2 (aq) <-> H2CO3 <-> HCO3- + H3O+ equilibrium. The water will be soft in as much as it has low levels of divalent cations Mg++ and Ca++, but it will be alkaline and have substantial bicarbonate. You definitely do not need to add any more KH, you already have lots.

Probably not necessary then, which is why we need @Andy Pierce etc.

HCl is very cost effective and also conveniently comes in well-defined liquid form - I like 1N (1M) HCl as a good balance between strong enough to not need crazy large amount and not so strong that it is serious health hazard (but you still have to treat it with respect).

Hydrochloric acid (HCl) it is then.

I'm no expert but I would imagine the pH isn't very stable anyway at 0 GH and especially 0 KH, wavering around 8 or 9 depending on slight additive fluctuations.

Exactly that, pH is a moveable feast whenever we are <"near pure H2O">.

Assuming that is all correct? Then pH will potentially always be unstable in soft, low conductivity water, because very small changes in water chemistry cause large changes in pH*.

*I'm staking my tattered reputation on this, but the <"toys are already poised by the pram edge">.

cheers Darrel