Ph ...

[ShinySideUp]

With all the talk of the aquarium cycle and how the pH affects ammonium and ammonia has made me wonder about my own tanks. The water straight out of the tap has a pH of around 7.3 or 7.4 but my tank water slowly falls to about 6.2 after a 35% water change weekly (it's a small tank so it's not a lot of water, probably around 40 litres changed at a time).

What causes the pH to fall? And does it matter (within reason) as lower pH values change less ammonium into ammonia?

I now have a bigger tank -- and a water meter -- so I don't want to change more water than is necessary.

Should pH readings be the same all the time? If not, what causes them to vary?

Never worried about this before and don't lose any fish but with the bigger tank comes greater responsibility.

Cheers

Martin

 

[coldcazzie]

Nitrate is acidic so it slowly causes the pH to drop in a tank over the course of a week.

PH is important, but less so than hardness. They are interconnected. The carbonate hardness will have a hand in how stable the pH is in your tank.

Trying to get the pH to remain the same will cause you a lot of stress and almost definitely have an adverse reaction on the fish - the pH buffers sold in shops are more trouble than they're worth and other methods need to be used carefully as they adjust the hardness of the water, and therefore the pH as well. If they're not used very precisely they can send the pH shooting up or crashing down which will definitely harm the fish. Keeping the water the same is more important than keeping it to a predefined number.

My tap water does a similar drop to yours - 7.4 from the tap but sits at around 6.2 in my tanks. I have very soft water, which explains the drop. I get around this by doing larger water changes rather than smaller ones: my weekly maintenance is around 60% rather than the 20-30% others may do. This way I'm replenishing more of the water so doing my best to keep the hardness the same.

 

[the_lock_man]

Quick follow up question, please Caz.

If you are taking out 60% of your 6.2pH water, and replacing it with 7.4pH, why is that not causing a pH shock to the fish? I appreciate the logic of why, and I appreciate that KH is more important than pH, but in absolute terms, isn't a large pH swing of that order detrimental to the fish?

 

[KISSfn]

Great question the_lock_man! Also your thoughts on adding a bag of crushed coral to filter please Caz?

 

[Bignose]

Quick follow up question, please Caz.

If you are taking out 60% of your 6.2pH water, and replacing it with 7.4pH, why is that not causing a pH shock to the fish? I appreciate the logic of why, and I appreciate that KH is more important than pH, but in absolute terms, isn't a large pH swing of that order detrimental to the fish?

pH shock is blamed for a lot more than it actually causes. Quite simply, fish in the wild undergo changes of 1 to 2 pH units a day all the time. A body of water with vegetation changes that much during a sunny day; the sun comes out, warms the water, temperature affects the pH, as the plant activity changes, the pH also is adjusted. Another example is a thunderstorm: bodies of water swell to twice or more their volume very quickly. Usually the pH of the runoff is not the same as the body of water.

In short, fish would not have survived long if the didn't have mechanisms to deal with pH changes quickly. And they do, they can change their internal pH by as much as 4 pH units when they need to.

Most 'pH shock' is really hardness shock. I have more info, but am on my phone now. Will try to post more when I get back to my computer.

 

[coldcazzie]

As Bignose said - pH shock is very hard to distinguish from hardness shock. I'm not really sure it exists, although I'm sure someone could produce evidence... A change from 6.2 to 6.8 or whatever it is after a water change isn't enough to kill the fish, or really even bother them. A change that small doesn't cause pH shock. Because pH is inextricably bound up with hardness it's very hard to give an example without linking the two....

Hard water has high carbonate hardness, and also high pH. Soft water has low carbonate hardness and low pH. It's very rare to get one without the other.

Because in terms of hardness the water in my tap is almost identical to the water in my tank, I can change large amounts of water and the fish won't be affected by the pH change. If I were to remove my soft water and add water from London (hard water), then the fish would likely be affected, but it would be because of the difference in carbonate hardness over the difference in pH. Yes the pH would be greatly changed in that situation, but it's importance is much less than that of the hardness of the water. But because as one rises the other rises it is difficult to be definitive about a causal relationship.

Sorry that sounds a little fragmented...

As for adding crushed coral to the filter, it depends on why you feel you need to.

 

[KISSfn]

I thought that adding crushed coral helped to keep pH stable.

 

[Bignose]

here is a long post where I detailed the mechanisms that cause hardness shock: http/www.fishforums.net/index.php?/topic/207210-acclimation-of-freshwater-fishes-to-the-home-aquarium/page__view__findpost__p__1726897

 

[coldcazzie]

I thought that adding crushed coral helped to keep pH stable.

Do you have especially soft water?

 

[BigbruiserAl]

Same as caz here. Tap water is approx 7.4 my tank water sits at 6.4 I change approx 200L each water change with no ill effects on the fish as explained above

 

[ian]

I wouldn't personally mess around with the Ph (adding coral), as others have said unless keeping certain Cichlids. Again, as above we focus a little to much on Ph, when we should be focusing on GH/KH, this is going to harm some fish more so. I remember reading somewhere (I think it was Heiko Bleher), that most fish will go through Ph changes throughout the day, going from 6.0 - 7.0 at some points in the Amazon basin.

 

[coldcazzie]

7.0 Ian, not 70!

 

[KISSfn]

I thought that adding crushed coral helped to keep pH stable.

Do you have especially soft water?

71.6 KH, 196.9 GH, Whatever that means!

 

[coldcazzie]

71.6 KH, 196.9 GH, Whatever that means!

71.6ppm is about 4dkh, which is about the same as my water (ie quite soft). You could add some, but it would involve a certain amount of experimentation to get the amount right, and in that time your fish might not be very happy. You'd want to be aiming for a given kh value, which would then lead to a more stable pH.

As I said before though, I'm not willing to do it so I simply do larger water changes to refresh the dissolved solids in the tank. I'm not the only member to do that due to soft water. It would be much easier and more suitable for you too. If your water was softer (0-2dkh) then perhaps I'd be saying different. But where it is, larger water changes should be sufficient.

 

[KISSfn]

Thanks Caz, ianho, BigbruiserAl and Bignose!