Reading GH/KH API test kit

[Cherrys]

I received the GH/KH liquid test kit from API today and I'm having trouble figuring out what exactly the numbers mean. If I'm reading it right we have hard water, which is what I was assuming we had. Could someone help me out please. Why would my tank be reading higher/lower? I did several water changes in the last few days. With the most recent one being yesterday (15% change).

My tap is reading dGH at 21 (350ppm?).
dKH is reading at 14 (250ppm?)

Tank is reading dGH 28
dKH is reading at only 12. I feel like I must have done something wrong, but it was 12 twice. Is there a reason the KH would be lower in the tank when the GH is higher?

Would pH level affect GH/KH at all? Usually the tank reads the same as the tap, but for some reason the tap is reading lower than normal.
Tap pH - 7.6/7.4 (high range)
Tank pH - 7.8

 

[StevenF]

How often do you do a water change and how much water do you repace when you do one? Insufficient water changes is common reason why the tank water will be harder than tap water.

The GH measurement is mainly a measurement of calcium (CA) or magnesium (Mg) salts in the water in the water. these can be Ca/Mg sulfate, chloride, or carbonate salts. However the KH test is specific to carbonate salts only and those may be a mix Calcium, Magnesium, Potassium, or Sodium carbonates. So your tests indicate some of your Ca and Mg is in the form of sulfate and Chloride salts while about half is carbonate salts. It is not unusual for Gh to be higher than KH. In other cases you could have most KH and little GH. So the ratio of GH to KH is not important.

If you PH is less than 7 it chan effect KH and GH. Limestone is a calcium carbonate rock. It only dissolves in acidic water (PH less than 7) PH above 7 is unlikely to have much affect on GH and KH. snail shells and Coral are also calcium carbonate.

 

[Cherrys]

I usually do about 30% every 2 weeks. Tank was understocked and is very understocked now (55gal/208L, with 6 cherry barbs).

We had some issues in the tank two weeks ago and I'm wondering if I need to keep doing smaller water changes to bring the tank back. Not sure exactly what got in the tank as parameters were all good, but there was major cloudiness that looked like a bacteria bloom and we lost almost our entire stock.

Would a bigger water change bring it back faster, or would that be more harmful to the fish?

 

[Essjay]

The KH can be lower in the tank than tap while GH can be higher.
The natural tendency of a tank is to produce acidic things - most fish waste products are acidic. Carbonates (KH) react with acids so KH is slowly used up.


Do you top the water up between water changes? Since only water leaves the tank, everything dissolved in the water remains in the tank. Adding more water also adds more hardness minerals so over time the amount of hardness minerals builds up.

Anything made of calcium carbonate (coral, shells, limestone etc) can slowly dissolve and increase hardness.


Bigger water changes would bring the water chemistry nearer to tap level. If in doubt, do a few small water changes every day for a few days, then start doing large water changes.

 

[Cherrys]

I will on occasion in the summer when it evaporates faster, but I have not done that in awhile. No added calcium carbonate that I am aware of. We only keep fish and I do not add anything to the water with the exception of Prime with water changes.

This is the first time testing the water so I cannot be 100% sure, but I'm pretty sure this is a fairly new issue. I do keep hard water fish, so maybe the added hardness was not a big concern for them? They were happy and breeding, but I will continue to do smaller ones for now and switch back to larger changes in a week or so, just to make sure I do not shock the remaining fish.

 

[StevenF]

Not sure exactly what got in the tank as parameters were all good, but there was major cloudiness that looked like a bacteria bloom and we lost almost our entire stock.

If you don't change enough water minerals can build up in the water and some of those minerals by trigger a bacterial bloom and or a fish death. We don't have enough information to know for sure if mineral buildup caused your issue.

Bigger water changes would bring the water chemistry nearer to tap level. If in doubt, do a few small water changes every day for a few days, then start doing large water changes.

I would strongly suggest doing the small water change and then follow up with larger water changes as Essjay suggests. Then after do regular water changes once a week and then adjust the amoutnt of water changed so that the water GH and KH stay stable.

 

[Cherrys]

If you don't change enough water minerals can build up in the water and some of those minerals by trigger a bacterial bloom and or a fish death. We don't have enough information to know for sure if mineral buildup caused your issue.

This is the first time ever that I have ever experienced cloudy water (I've been keeping fish for over a decade), and I always do water changes in the same way. The cloudy water happened after a water change where one of two filters were accidently thrown out. I assumed this caused a mass bacteria bloom due to a significant reduction in BB, but my parameters (ammonia/nitrite) were always zero. Would a bacteria bloom cause those to rise or not necessarily? I thought it was bacteria at first, but when parameters were stable I thought it had to be something else. My tanks are usually understocked though, so maybe the remaining stock was not too much for the BB in the second filter. The cloudiness went away in about 6 days, but I couldn't do water changes as that made it worse. The fish that were still in the tank seemed unaffected by the cloudiness after day 2 so I figured it was okay to let the tank work itself out, since the fish seemed okay.

I will continue to do small changes this week and then go back to normal changes after checking tank parameters. Hopefully by then the readings will be similar enough to the tap that I can switch back without shocking the fish.

 

[Essjay]

Bacterial blooms are caused by a type of bacteria which live free floating in the water and feed off carbon based foods (the filter bacteria feed off nitrogen based foods). They won't cause ammonia or nitrite in the water.
Bacterial bloom can also occur if you do an extra vigorous water change and stir up a lot of organic debris (fish poop, uneaten food) from the substrate.

Water changes don't usually get rid of bacterial blooms as these bacteria multiply very fast and those left in the water you don't remove soon make up the numbers. It's usually a case of waiting till all their food is gone, then they die.

 

[Cherrys]

Good to know. I did not realize the bacteria were different.

I did two smaller changes yesterday and when I checked GH (several hours after the last change) it was only 3 degrees harder, so I think I am almost there. In regards to the build up of minerals, do they stay in the water column or will they settle into the substrate? I gravel vac with every water change, but was wondering if that was absolutely necessary during these smaller ones while I fix the hardness issue.

 

[Essjay]

The hardness minerals are dissolved in the water, they don't settle on the bottom. Sometimes you get a strip of them at the top of the water line where the water has evaporated leaving the minerals behind, but that's the only time you get solid particles of the minerals.


As for gravel vacuuming, it depends how messy it is. If it's very messy it will take several cleanings to remove all the debris but if very little comes out you don't need to do it every time.