Low kh, high gh

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Stormyrose786

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Mar 10, 2020
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Cassie
So, I have this problem off & on.

My kh sometimes gets low, but that's easy to fix with a water change using tap water. And if it's high, which is rare, I can lower it using a mix of RO water & tap. No problem.

But lately, sometimes my kh is low, but gh is really high. So I do small water changes to increase the kh, but am always afraid the gh will go higher, also. So I use a water softener pillow to keep that from happening.

My other parameters are almost always good, including ph.

So here is the question...is there a way to raise kh without raising gh? I can't really find a clear answer for that.
 

fishorama

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What is your tap water KH & GH? Is it different at different times of year? Do you have live plants? How many fish in what size tank? What do you consider "good" for all parameters? Do you have rocks (like limestone or real coral) that may add to GH? Fertilizers?

I never worry about "high" KH, my last 2 houses have "soft" water (low GH & KH both). I use a bit of crushed coral for both but if you GH tends to be "high" that might not be the best answer for you.

I have used a little baking soda to raise KH BUT it does add sodium that can build up without large regular water changes. Measuring sodium is a different thing for us freshwater fish people...I think it's potassium carbonate (or bicarbonate?) that raises KH without adding GH or sodium...I'll have to look it up...maybe tomorrow...sorry, close to bedtime.
 

fishorama

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Oops, I didn't search today, a busy day...but you could Stormyrose...

To really help we need all your tank & tap parameters plus fish & other tank decor...
 

Stormyrose786

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Hi, sorry...completely forgot that I even asked...

But thanks for responding...

This happened in my 20g last time I did wc, but it is usually my 10g, & I should also mention, it's only been doing this the past few months.

Tonight, my parameters (10g) are:

pH - 7.0
Ammonia - 0
Nitrate - 0
Nitrite - 0
KH - about 60 ppm (4 drops)
GH - about 200 ppm (11 drops)

By drops, I mean how many drops I put in the water sample before the color turns - I use API Master Test Kit & API liquid tests for KH & GH.

What I consider good parameters is -

pH - 7.0 - 7.6 (it usually is 7.0 or 7.2)
Ammonia - 0
Nitrate - 0
Nitrite - 0
KH - 100 - 200 ppm
GH - 100 - 200 ppm

I have all guppies in that tank, gravel, plastic plants, decor from the store...but I've had all this for about a year & a half, & it only just started having consistent low KH & high GH.

What I have been doing is changing 25% using filtered tap water. The KH goes up to about 80 or 100 - Idk - it's 5 drops, sometimes 6, but then goes back down to 4. So it stays mostly between 50 to 100 ppm.

So the KH has been low in the past every now & then, but a wc would bring it back up. My GH used to stay below 200 ppm (maybe 8 or 9 drops), so using tap water was never a worry before.

And actually, I only ever had to lower my KH when I had tetras with the guppies. I could actually keep it right at 100 ppm, but every now & then it would go up a little & then I would mix RO water with filtered tap water, & it would go back down.

Oh, & I have 7 adults in the 10g. Just found 6 babies yesterday.
 

Stormyrose786

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For my tap water -

KH - about 180 ppm (9 drops)
GH - about 200 ppm (12 drops)

So on exact ppm numbers, I'm estimating, because all I really have to go by are ranges. And like I said, I want both to stay between 100 (6 drops) & 200 (11 or 12 drops) ppm. My KH is staying below 100, my GH is staying right around 200. I would like to do a 50% wc, but I am afraid my GH would be really high then.

Btw, I try to do wc once a week, but it doesn't always happen that way.

And we have too much lime in our tap water, which is why it is like it is.

One thing I think might help is to do a 25% wc each day until it goes back to where I want it. But I have not been able to do that yet, for various reasons.

So basically, I just want to get my KH back up above 100 ppm, without raising my GH.

Should I just try to do the daily wc, or am I missing something?
 

Stormyrose786

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Goodness...my sense of time has been way off with all that's going on...I'm sorry...it only has been doing this for about a month, not a few months.

I still would appreciate any suggestions - thanks!
 
Apr 2, 2002
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First, I am unsure about what your regualr water schedule is. How often and how much water do to normally change.

The real question is why is the KH dropping? In a tank there are a few things that use the carbonates/bicarbonates whoch pretty much constitute KH. Some live plants can do this, but you do not have any.

The next thing that can burn though KH is the cycle. The bacteria need inorganic carbon and they can get this from cabonates/bicarbonates. The cycle itself is acidic. This is one of the big contributors to "old tank syndrome."
(Note: All quotes below are from https://fins.actwin.com/mirror/begin-chem.html#altering )

the nitrogen cycle produces nitric acid (nitrate). Without buffering, your tank's pH would drop over time (a bad thing).
So, if you are well stocked and need a lot of bio-filtration, you have a lot of bacteria using up a lot of carbonates. One way to know what is going on is to test the pH

I am not a fan of water pillows:

Typical home water softeners soften water using a technique known as ``ion exchange''. That is, they remove calcium and magnesium ions by replacing them with sodium ions. Although this does technically make water softer, most fish won't notice the difference. That is, fish that prefer soft water don't like sodium either, and for them such water softeners don't help at all. Thus, home water softeners are not an appropriate way to soften water for aquarium use.

Fish stores also market ``water softening pillows''. They use the same ion-exchange principle. One ``recharges'' the pillow by soaking it in a salt water solution, then places it in the tank where the sodium ions are released into the water and replaced by calcium and magnesium ions. After a few hours or days, the pillow (along with the calcium and magnesium) are removed, and the pillow recharged. The pillows sold in stores are too small to work well in practice, and shouldn't be used for the same reason cited above.
Not all water softeners use salt. However, the alternative to a salt based softener is mostly designed to prevent calcium buildup in pipes. A salt-free system works by crystallizing calcium, but not removing it. So you need to know which system you have before you start ysing Sodium bicarb. If your softener is adding sodium, you need to be careful about adding more.

Here is the info on using both calcium carbonate and sodium bicarbonate (baking soda):

Hardening Your Water (Raising GH and/or KH)
The following measurements are approximate; use a test kit to verify you've achieved the intended results. Note that if your water is extremely soft to begin with (1 degree KH or less), you may get a drastic change in pH as the buffer is added.
To raise both GH and KH simultaneously, add calcium carbonate (CaCO3). 1/2 teaspoon per 100 liters of water will increase both the KH and GH by about 1-2 dH. Alternatively, add some sea shells, coral, limestone, marble chips, etc. to your filter.

To raise the KH without raising the GH, add sodium bicarbonate (NaHCO3), commonly known as baking soda. 1/2 teaspoon per 100 Liters raises the KH by about 1 dH. Sodium bicarbonate drives the pH towards an equilibrium value of 8.2.
(100L =26.42 gal.)

When I did my high tech planted tank and was adding pressurized co2 I worried about a pH crash caused by the the acid from the co2 using up the KH. I did not want to raise my GH. so I used a small amount of crushed coral in a bag in my filter. It amounted to about 1/2 cup for around 30-36 gals of water. It dissolves over time and needs to be repelenished. A small amount did not moe my GH. This works a bit slowly at first and then should level off. When things start to slide backwards its likely time to replenish the coral.

Finally. the conversion factor from KH or GH dg to ppm is about 17.8. This means that when you read 9 dg (drops) for KH, your ppm is at least 143 and a max of 177 ppm. ( 8 dg 17.8 x 8 =142.4 and 9 dg = 160.2, but if your KH is say 155 ppm that is over 142.4 but under 160.2. So it should still read as 8 dg. I cannot say this is factually correct because i do not know how accurate the KH test kit is in terms of ppms nor where the brak points are for each added dg.)

Here is what I suggest you do. When it is time for the next regular wc, test both KH and GH. The do the change and test again in about 15 minutes which gives the water time to circulate and mix. You know you are using up KH, but what about GH? If it is dropping some between changes, then you may not need to worry about them raising the GH much if at all.

Finally, pretty much any tank which does not have any live plants should almost never have 0 nitrate. This is also the worst or all the tests we use. The nature of the reagents, especially in bottle #2, is that they precipitate out of solution. This means they becomes solids, sink to the bottom of the bottle and stay there. They need to be mixed back in. Doing this means shaking the bottle hard, then banging the bottom on the table a few time and shaking it hard again. Also shake bottle #1 well but it is not as bad no banging the bottom is needed. Measuring nitrate is problematic in general. the API kit works by converting it nitrite and then measuring that. It is considered to be least accurate between 0 and 20 ppm. That does not mean it is not a useful test. But you must be sure to do the above to bottle #2.

So I am not sure your nitrate results are accurate. Just in case, also please check the expiration dates on your test kits. They should be fine but let's be sure.
 
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