Kh 2 & Gh 5...what Does This Mean For My Tank?

[Lazerus]

Hi all…

I’m still trying to get my head around pH and its relationship to gH & kH….

From my tap currently:
pH 7.6
kH 2
gH 5

Yet, my water in my bigger tank reads:
PH 6.8 or 7…it’s hard to tell the difference.
kH 2
gH 5
Also:
Ammonia:0 pmm
Nitrite:0 pmm
Nitrate:5 ppm

This is after a week since my last 20% water change.

Is it right that the kH and gH still the same? Should I not see some change in the readings?

I do weekly water changes on my 22gal, just out of habit from having a 10gal...but the noticeable difference is that my bigger tank so far has never gone over 5ppm in Nitrates...its often less actually.

This has a bearing on the kH and gH too, doesn't it...and because the readings of nitrate is low, that is why I don't see any changes in the kh & gH? Right?

So....does this also mean that I can leave my bigger tank for longer without water changes?

Like, I'm wondering should I be only changing the water when I see it hitting 10ppm or 20ppm even?
(That might take a few weeks I imagine though...not sure if I'd feel right about leaving it that long...but on the odd occasion is it safe to do that though? )

The thing is, I’m worried that because of my low kH that I’m going to face a pH crash…I’m trying to be ‘on top’ of that by knowing what my kH is all the time, and doing very regular, frequent water changes.... but as it isn’t changing, should I let my guard down leaving me free every now and again to miss a week sometimes?

You see, I’m going away tomorrow, and I am now facing this particular dilemma...so I’m worried that the tank will face this ‘impending’ pH crash while I’m away…. should I be worried?

What do you think?

 

[waterdrop]

First of all Laz, I think you are worrying too much! Your water parameters seem excellent and the fact that KH and GH stay nice and steady is a GOOD thing! (When people say fish don't like the pH changed on them, what they really mean, whether they know it or not, is that fish don't like the -hardness- changed on them too rapidly!) Also, I think you are describing good instincts about your maintenance habits, even if you have a little confusion about the whole nitrate/hardness/maintenance thing, as described.

I would suggest a slight difference in how you view the relationship between nitrate(NO3) measurements and the percentage/frequency of maintenance water changes you do. You don't do water changes -because- of high nitrates, you do them regardless. The practice of recommending a water change when people report nitrate as being high is something we do here in the forum because nitrate can be an -indicator- of someone not doing their water changes. You shouldn't view it as a ticket to not doing water changes just because NO3 is staying low.

Water changes accomplish a slew of things, most of which we don't measure. Its true that some nitrates(NO3), nitrite(NO2) and ammonia(NH3/NH4+) are taken out with each water change. But much more interesting is the fact that any buildup of heavy metals and organic compounds (DOC-dissolved organic carbon, stuff like that) is also taken out, giving the tank a "reset" as it were. (Our water has thousands of things in it and we just measure 3 or 4, its not just pure water with those 3 or 4 things!) And plant fertilization works the same way ideally - the ferts are dosed in over the week, they start getting a bit too high and then the water change "resets" them at week's end. Now even more interesting still is that tap water itself turns out to be a great source of good stuff like calcium and magnesium and other traces that are on the good side of things. They are nutrients to the plants and they are very necessary for things like osmotic cell pressure balance in the fish. So water changes accomplish lots of taking out of bad stuff and putting in of good stuff, regardless of what our basic tests say.

OK, now does this mean you should freak out about a weekend trip that means you miss your water change. No, I think not! What's important is the habit, the majority of the time behaviour. If you miss one you might be able to do a smaller one during the weekdays, or you might just have to wait for 2 weeks without a water change. It shouldn't be too bad in the vast majority of cases.

And one more thing Laz: I think you might be remembering how strongly pH was pushed down during the cycling when you worry about your pH taking a crash. After cycling is over, there is considerably less downward pressure usually, because you are not dumping 5ppm of ammonia in there and getting a ton of acids out the other end of the system that use up your buffer (your KH) so fast. Your fish load is probably producing a lot less than 5ppm and that's evidenced by your low NO3 levels that seem pretty stable. That's why your tap water KH (2) stays the same in your tank (KH=2). Its just not getting used up by the very slow production of nitrification acids. And yes, you are directly seeing what we talk about when we say that larger volume tanks are more stable than lower volume tanks!

Hope this will help, even if you have to read it a couple times to understand all the chem gibberish

~~waterdrop~~

 

[Lazerus]

Thanks Waterdrop....

Ok, I've read and re-read....and I'm feeling alot happier. Phew!

Yes, you are quite right about the whole 'fishless cycling ph crash' thing being still prominent in my mind....that is whats causing me my anxiety I think! I'd forgotten a few of the basic rules surrounding it all.

I just needed to be reminded again (and again..... ) about things being totally different when the fish are in the tank slowly releasing waste as opposed to the 5ppm of household ammonia!

For some reason I have it in my head (I must have read it somewhere) that once the kH dropped below 4, that I was to watch out for a crash...and as my water was at a kH of 2 I was panicking and trying to be really vigilant about watching it....and as nothing ever happened, I was getting confused!

So, I was just wondering when would I expect this 'turn of events!'....

Ok so...great! I won't be slacking off on the water changes...it just not in my nature...I enjoy it! But I did wonder would I be able to get away with it every now and again, especially a week like this one.

(I've actually just done a 30% 'going on holidays' water change, just in case of any eventualities, in between browsing this forum! Now that's what I call multi-tasking eh!)

Anyway, as always...Thanks for all the great, detailed advice. I've learned loads in just one sitting!

 

[Colin_T]

When the KH drops to 0 is when you see a sudden pH drop. The KH (carbonate hardness) stops the pH from dropping too rapidly. As things break down in the water (ie: ammonia to nitrite & then to nitrate) they produce nitric acid, which will lower the pH. Carbon Dioxide (CO2) will also lower the pH because it is acidic. These acids are kept in check by the KH in the water. When all the KH is gone, the acids will drop the pH.
If there is lots of food going into the tank, or if you have a CO2 unit running on the tank, the KH could drop very rapidly. However, if you only have a few fish and are feeding sparingly, the KH & pH could be fine for weeks without any major change.
It's all about water volume and the amount of fish food being added to that volume of water. The more water in the tank and the less food that is added, the slower the KH will be used up.

You can do bigger water changes if you like. 20% is a general guideline, but many people do bigger changes. I used to do 75-80% water changes each week due to the high number of fish in the tank, and the huge amounts of food that were fed to them. The main thing to consider when doing water changes, is to make sure the new water is free of chlorine/ chloramine before it is added to the tank. Also try to have the new water at a similar temperature & pH to the tank water. It doesn't have to be exactly the same just similar. Then you can do a 40 or 50% water change without any problems.

 

[Dave Spencer]

When the KH drops to 0 is when you see a sudden pH drop. The KH (carbonate hardness) stops the pH from dropping too rapidly. As things break down in the water (ie: ammonia to nitrite & then to nitrate) they produce nitric acid, which will lower the pH. Carbon Dioxide (CO2) will also lower the pH because it is acidic. These acids are kept in check by the KH in the water. When all the KH is gone, the acids will drop the pH.
If there is lots of food going into the tank, or if you have a CO2 unit running on the tank, the KH could drop very rapidly. However, if you only have a few fish and are feeding sparingly, the KH & pH could be fine for weeks without any major change.
It's all about water volume and the amount of fish food being added to that volume of water. The more water in the tank and the less food that is added, the slower the KH will be used up.

You can do bigger water changes if you like. 20% is a general guideline, but many people do bigger changes. I used to do 75-80% water changes each week due to the high number of fish in the tank, and the huge amounts of food that were fed to them. The main thing to consider when doing water changes, is to make sure the new water is free of chlorine/ chloramine before it is added to the tank. Also try to have the new water at a similar temperature & pH to the tank water. It doesn't have to be exactly the same just similar. Then you can do a 40 or 50% water change without any problems.

CO2 + H2O <=> H2CO3

How is this dropping the KH?

Dave.

 

[Lazerus]

Thanks Colin...

You've just reminded me about another reason I was concerned about the kH dropping.

I also use CO²...

How is this dropping the KH?

Dave.

I did have it in my head that using CO² brings your kH down....I'll see if I can find an article on it...

I'm not going to debate it with you though....as clearly I'm a newbie to all of this. I leave that up to the experts!

 

[Lazerus]

Good article here about the pH-KH-CO2 Relationship...might answer a few questions?

http/www.csd.net/~cgadd/aqua/art_plant_co2chart.htm