Hardness: does this make sense

seangee

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While on the Pozzani site to re-order nitrate reduction cartriges I spotted this https://www.pozzani.co.uk/product_info.php?products_id=184. I bought a cartridge to try since I am already filtering my tap water so its no additional effore or time..

Tonight I did my usual 100 litre change (180 litres in the tank) and after the water change my readings (using JBL strips) were:
GH: 16d
KH: 20d
pH: 8 (these are all what I expected them to be)

Then I filtered another 25 litres using the softening filter in addition to the nitrate and carbon filters. I haven't put this into the tank but in the bucket the tests showed:
GH: 4d
KH: 18d (midway between 16 & 20)
pH: 7

Does that make sense? I would have expected the KH to drop by more given how much the GH dropped. pH was straight out of the tap so I'll check that again in the morning once it has stood overnight.
 
In order to manage hardness in your aquarium it is generally recommended that the best solution is to fill your aquarium with soft water, and then add a buffering product to set the hardness to the required level (such as calcium carbonate, available from most pet stores). This means that as you top up or change the water in the tank, you are not adding any additional hardness, and the levels will remain reasonably constant over time.

and then add a buffering product to set the hardness to the required level
This bit is correct, you need to reminaralize the water to your requirements.

it is generally recommended that the best solution is to fill your aquarium with soft water
This bit is not correct, You should alway mix the water and remineralizing salts in a bucket or drum before adding it to the tank to avoid PH swings.
 
This bit is correct, you need to reminaralize the water to your requirements.
...
This bit is not correct, You should alway mix the water and remineralizing salts in a bucket or drum before adding it to the tank to avoid PH swings.
Not really bothered with either of those things as I will only use it to cut my tap water so certainly won't be adding minerals back.

Question was about the fact that GH reading incorporates KH so is it feasible that the GH has dropped so far when KH is still so high. I.e. it seems to have produced very soft water with high alkalinity ????
 
Making more sense now.
Tested the jerry can water this morning and read the strip in sunlight. Then retested using a different brand of strip with the same results. Last nights test was out of the filter fairly early in the process so the resin may still have been flushing through.

Results are
GH: 7d
KH: 14d
pH: 7.2

Have now added 25 litres to the tank. Obviously not expecting a massive change as that's only around 15% but I'll test this evening and possibly do a few more 10-15% changes over the next week to allow acclimation. I think I'll aim for a target of 12 dGH. The fact that the KH is still relatively high should mean that I can just let the pH find its own level and it should remain stable.

P.S. The water tastes a lot better than what is produced by my under sink kitchen filter :band:
 
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If you are using an ion exchange resin or something along those lines, it is probably remove the chlorides from the water but leaving the carbonates. This will reduce the calcium & magnesium chloride that makes up GH, and leave the carbonates and bicarbonates that make up KH.
 
it is probably remove the chlorides from the water but leaving the carbonates.
Now that was so much easier to understand than some of the technical papers google led me to - which said the same thing using a lot more big words :cool:
 
There are 2 types of ion exchange resin - anionic and cationic. Anions are negatively charged ions such as carbonate; cations are positively changed ions such as calcium and magnesium. Calcium and magnesium are the ions measured as GH.
If the resin in the Pozzani filter is cationic they will exchange calcium and magnesium for another cation, typically sodium or hydrogen ions. They won't remove carbonate or any other anion such as chloride.

Unfortunately, the Pozzani website does not say what the ion exchange resin is, whether it is anionic, cationic or both. Or what they exchange the ions for.



The type of resin that swaps calcium and magnesium for sodium is used in a lot of water softeners. This type of softener is not good for fish as it adds a lot of sodium and, with the possible exception of Rift Lake cichlids, freshwater fish have not evolved to cope with a lot of sodium in the water.
The hydrogen ion type of exchange resin is found in things like Brita filters. Because these add hydrogen ions to the water, they lower the pH (pH is an upside down measure of the amount of hydrogen ions in the water). When I had a Brita jug I tested the water. It dropped the pH of my tap water from 7.6 to off the bottom of the scale.
 
I have emailed them to ask for clarification, and won't add any more until I have a response. i did (perhaps naively) assume it did not use sodium as its sold as an aquatic product and would be of no use to marine fish keepers.
I do know that there are resins that will swap potassium for calcium and assumed that this is what is being used.
 
Update: spoke to one of the guys at Pozzani earlier in the week and he was very helpful. The resin is cationic and uses hydrogen for the exchange so is safe. The reason I haven't seen a massive ph drop is because the KH is so high. PH has stayed fairly stable but KH is dropping gradually. I will add the 4th 15% wc this evening and suspect that will reach my target and then continue to cut the tap water with 50% filtered water.

He did confirm that they use puralite resin. I may buy this in bulk if the cartridges don't last a reasonable time as I don't really fancy recharging with acid at home.
 
That makes sense of your figures in post #1. The hardness filter removed a lot of calcium & magnesium ions, resulting in a much lower GH. The calcium & magnesium ions were swapped for hydrogen ions. These reacted with some of the carbonates in the water resulting in a slightly lower KH. The extra hydrogen ions also lowered the pH since pH is an upside down measurement of hydrogen ions.


The reason that the Brita filter I mentioned in post #7 dropped my pH so much is that I have soft water with KH 3. Besides the pH dropping off the bottom of the scale, my KH was zero in the filtered water.
 
what sort of acid do they recommend to recharge it?
They don't - it would affect sales too much if everyone knew. AFAIK any acid will do but most seem to use HCL or H2SO4 - presumably because they are easily available (as pool acid).
 
That makes sense of your figures in post #1. The hardness filter removed a lot of calcium & magnesium ions, resulting in a much lower GH. The calcium & magnesium ions were swapped for hydrogen ions. These reacted with some of the carbonates in the water resulting in a slightly lower KH. The extra hydrogen ions also lowered the pH since pH is an upside down measurement of hydrogen ions.
From my original readings:
GH: 16d
KH: 20d
pH: 8

I have done 3x 15% changes and my tank is now
GH: 12d
KH: 15d
pH: 7.2

Remember I'm testing with strips so those figures are not completely accurate but the trend is where I want it to be. I'm pretty happy with those results. As I have another jerry can ready filtered I'll put that in this evening and then add 50/50 mixed water from my next w/c this weekend.

FWIW the guy at Pozzani said its not legal to sell drinking water systems in the UK that exchange sodium ions (but acknowleged that some do).

For anyone reading this and considering something similar please note @essjay 's comments. This works for me because I have a very high KH. KH is also referred to as alkalinity and buffers pH. There is a very real risk of a pH crash if you don't have a high KH to start off with - especially if you use a high percentage of filtered water, so make sure you test the combined result.
 
Did my final 15% change on Wed and then my usual 60% change this morning. For this morning's change I used 50% softened water with 50% tap water.
Numbers 12 hours after the W/C were exactly the same as immediately before:
dGH: 10-12
dKH: slightly under 15
pH: 7.2

I am happy with these results and expect my params to be relatively stable from now on but will continue to monitor.
 
They don't - it would affect sales too much if everyone knew. AFAIK any acid will do but most seem to use HCL or H2SO4 - presumably because they are easily available (as pool acid).
LOL.

would white vinegar work? it has a pH of around 3 and is safer to handle than pool acid, it might be cheaper too.
 

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