Confusing Water Test Results

[LauraFrog]

Okay, NOW I'm confused. I'm sick of stuffing around in the dark where water hardness is concerned. I've always suspected it's very soft based on off the chart readings on strip tests, but I know they're rubbish so I bought an API gH/kH test.

The water I tested is tap water, which is pumped from the creek, and does not have anything (chlorine/chloramine/alum) added. The samples were taken from the same tap, at the same time. I followed the instructions to the letter.

kH: First drop turned the sample blue. Second drop turned it green. On three drops it was yellow. This is a reading of 3 degrees/57ppm.
gH: First drop turned it orange. Second turned it green. This is two degrees.

This is an API test, brand new out of the box! I don't know what's wrong with it, but I was confused enough before... I was under the impression that it was impossible for gH to be lower than kH (basic chemistry: my understanding was that kH was a measure of ionic calcium, while gH measured calcium AND others such as magnesium, therefore at a minimum gH and kH must be identical.)

I will retest and post the results in case I made a mistake, but I haven't got the test solutions mixed up, they look totally different. As far as I know the solutions have not been heat or light affected but nobody mentioned that these ones were photosensitive... made that mistake once with a phenol based ammonia test and now I'm very careful with my reagents... they are too expensive to ruin.

I think I'll also test my brackish tank, the salt I add to that increases the hardness.

 

[waterdrop]

I believe you are between the margin of error of the tests themselves and of interpreting what's going on with the drops. You have to remember that all these tests are a bit crude and its perhaps best to just grab the take-home message which in your case is that your carbonate hardness is too low to do much buffering of pH at all. (Don't mean to be oversimpifing, know you may have some other uses for your numbers )

~~waterdrop~~

 

[petertr]

Your water is so soft, its difficult to measure.


I guess your pH is very low too? You may want to consider putting some crushed coral in your tank.

 

[LauraFrog]

Okay, I'm starting to think the test is faulty. The pH of the water as it comes out of the tap reads at 7.4 on four separate tests (bromothymol blue independant, universal indicator independant, API freshwater master, API freshwater master high range).

I just tested the water in my 23 gal... I was planning to add salt and rift lake conditioner, I'm planning on converting it to brackish (mollies, platys, bumblebee gobies.) kH tested as one drop... seriously, the test solution turned pale yellow on the first drop I added. Then the gH took eleven drops. Eleven... that's, like, really, really hard water. The tank runs on an undergravel with inert pea gravel, contains bogwood (which might lower the pH but I don't see how it could increase hardness) and an oversized internal power filter with ceramic noodles in it - now if they were going to do anything, surely it would be kH? The pH in this tank is about 6.8-7, which I figured was normal because it's an undergravel system and there is staining wood in there.

I do add plant ferts which do include magnesium but they are never overdosed and I do water changes at 50% a week (the bottle recommends 10% a week to 'stop trace elements building up to harmful levels' but I do more than this anyway because the tank was a bit overstocked before).

I also don't understand how the water COULD be that soft, because it comes from a large irrigation dam supporting a very large range of species, including the pest fish Tilapia, known in the hobby as mozambique mouthbrooder. (Yep, an african cichlid...) The strips were reading water hardness as undetected, so I sorta went, oh, yeah, whatever, stupid things are inaccurate anyway. But now the results from the API kit are all over the place.

Do you guys agree that it's faulty? The 23 gal is filled from the same water tank as the water I tested last night... I don't think that anything in the tank could have caused this gigantic discrepancy.

 

[petertr]

Right, you just said the KH was 1 - thats carbonate hardness.

GH is TOTAL hardness - this should always be the higher number of the 2. Your pH of 7.4 would indicate there is some hardness in the water.


If it helps, my GH is about 25-30!!

 

[waterdrop]

Yes, I believe one way to think about KH versus GH is to think of them as tests for different mineral compounds that are dissolved in water. They each measure separate ones of these.

So KH measures the calcium ions and bicarbonate ions in water (carbonate hardness, also historically called temporary hardness because you could "boil out" these particular mineral compounds.)

Whereas GH measures calcium sulfates, calcium chlorides, magnesium sultates, magnesium chlorides and other less common mineral compounds (general hardness, also historically called permanent hardness because you couldn't "boil out" these particular mineral compounds.)

So you could indeed have low KH, but high GH, it just depends on what's in your water.

The one city listing in QLND, Aus., that of Brisbane, did seem to show quite low KH but GH of 5, not as high as yours, but higher than the KH.

~~waterdrop~~

 

[OldMan47]

Your general hardness will have been increased by the fertilizers you have added and also by being concentrated by water evaporation. The ferts add it directly. The water evaporation means that all the minerals are left behind while the water evaporates and of course even the low hardness you put back adds some minerals back in. If you don't do frequent large water changes, your hardness can go through the roof this time of year when evaporation rates are high. At 50% every week it is probably not a big contributer to your GH like the ferts are. Magnesium compounds are registered as GH as are any calcium compounds. Since much of what is added is one or the other of these, it will raise the GH considerably.

 

[LauraFrog]

Okay, thanks for the help! I will have to restest some of the original samples, there is of course a possibility that I have screwed up some of the tests, but I'll check again.

I'm worrying about this because I really want to keep mollies, apparently they sell really well (moneymaking scheme, and besides I love them). It's the big sailfins that everybody wants and all my attempts to keep them in soft freshwater (or with a teaspoon or so of salt per gallon) have been abortive, with them being plagued by columnaris, ich, fungus and finrot that never affected anything else. I ramped up a bit more salt in there yesterday... it's marine salt I'm using, not aquarium salt, I figured that it would include some hardeners in it and result in me going through less rift lake conditioner which costs the ends of the earth.

The 50% weekly water changes come pretty much standard with water this soft because I find I have problems with acidification if I don't do it. It has never bothered me because it's a lot easier to do water changes than mess around trying to balance the hardness, especially since I can't get stuff like crushed coral. I've just chosen soft water species and soft raised platys. Since I'm going to make that tank hardwater I might cut down to about 30% weekly. What do you think?

 

[OldMan47]

It sounds right to me Laura. If you are pushing the water to gain hardness and pH by using calcium carbonate, typical of marble or limestone, then 30% water changes should be more than enough. Once you get your water stable and higher in calcium than previously, you can expect the mollies to do better. My water runs about 12 degrees of KH and GH so I never have your particular problem. Mine is usually how to get hardness low enough to breed corydoras.