Ph Increase .... Why?!

[Dazzler666]

Hi all. My partner has a 90ltre tank with guppies, harlequin rasboras, galaxy rasboras and two baby bristle nose plecs. A few days ago she found that several of her guppies are now pregnant and two of them gave birth to fry which we have now moved to a different tank. Now, she does weekly partial water changes however today some of the rasboras looked pale. She has done a water test with an API master kit and the readings were
Ammonia 0
Nitrites 0
Nitrate 5
PH which is usually around 7.5 has increased to 9 . Why we have no idea!!!!
Any suggestions as to what could cause this?
She appears to have suffered some losses too but all seemed present & fine yesterday and earlier today so we are at a loss as to what has happened .
We are going to do a large water change now but any help-advice would be very much appreciated.
Cheers,
Darryl.

 

[mattlee]

have you tested the water from the tap at all?

have you added any new items into the tank recently, like new substrate or decor etc?

do you use any chemicals in the tank? if so what?

 

[Dazzler666]

No haven'tt tested the tap water PH but if has been running at 7.5 for weeks. My misses added 2 guppies and -5 galaxy rasboras a week ago, in that time the guppies got pregnant and had fry and all has been well until today!! She also added some elodea densa plants which were rinsed in warm water prior to adding to tank.
No chemicals added except Esha minerol when water change done a week ago.
Was thinking about adding a preventative dose of ESHA 2000. What do you think?
Fish getting colour back after substantial water change! .
Just confused as all other readings were fine except the PH.
Thanks for the posts though, much appreciated.
Darryl

 

[FishBlast]

Is there any limestone in the tank?

 

[OldMan47]

Sometimes a local water authority will raise the pH either intentionally or not. If your local water supplier uses a lime softener and it gave them any trouble, the excursion will have caused some lime to carry over into the outlet water. That would mean an extreme pH excursion. They would be under no obligation to tell you about it because the only effect, from their point of view, would be a slight flavor change for human consumption. Unfortunately, the priorities of local water authorities has nothing to do with fish keeping needs.

 

[Dazzler666]

No there is no limestone in the tank bud. Thanks old man though doesn't surprise me about water authorities!! If there is a sudden PH increase is there a quick way to lower it again, apart from a water change?
I've read that basically lowering PH can be very difficult and is not advised unless necessary.
Thanks for the advice.
Oh thankfully my other half only lost one guppy.

 

[OldMan47]

I am surprised that any fish were lost. Fish are far less sensitive to pH than we ordinarily give them credit. The only way that I know to drop the pH would be a massive water change. Before you do that, measure your tap water pH. There is little point to removing 9.0 pH water and replacing it with more of the same.

 

[Dazzler666]

Previously when we tested our tap water it was a PH of 7 though haven't tested this time.
So my understanding is that if the water authority to increase the PH by adding chlorine, etc there is no simple or quick way to lower it when put in the tank?! The fish have to endure?! .
Thanks again for the advice, I learn something new everyday!!!

 

[CezzaXV]

Pretty much. There are ways of lowering pH, but to be honest they're going to cause you more trouble than just leaving it where it is for the time being. The pH probably won't be affecting your fish directly, but it may harm them if you did a large water change with pH 9 water when the water was previously 7.5.

I would advise you to test your tap water though since you have the means to do so. It may turn out your tap water is fine, then we need to start looking for another cause.