pH changes

[wondabread]

The tank I am having problems with is a 75g freshwater. Sand substrate, some rocks, plants (rotala indica, anacharis, bacopa, java fern, onion plants) 6 tiger barbs and a few guppies left over from cycling.

My question is has anyone had play sand affect pH in a tank? I am in the process of testing all my rocks in buckets for pH changes. I did the vinegar test and had no bubbling.

I am running a magnum hob canister and a fluval 405. All the fish are thriving, but the plants are not. Tap pH is 7.6, tank pH is somewhere around 8.4-8.8. Something in this tank is changing my pH.

Thanks

[Whiskers]

Fill a small glass with tap water and let it sit for 24 hrs and test it. you can probly get away with testing it in 2 to 4 hrs but i would let it go for 24 to be sure. your tap water might be doing what mine does.
someone told me that it could be my tap water has co2 gas (co2 gas causes ph to be lower) in it when it comes up but gasses off (as co2 gasses off, the ph rises) after a period of time till it reaches it normal state. mine out of tap is 7.4 and in tank is about 8.2. i'm not sure if this is the answer but its worth a check.

[Pure]

It's probably your tap water after it out-gases the CO2 that gets built up in it in the lines. Let some sit in a glass for 24 hrs and test that. Take your results and go from there.

That is a pretty large jump, but you still need to make sure if this is the case.

edit: Jinx whiskers

[iapetus]

Originally Posted by Whiskers

someone told me that it could be my tap water has co2 gas (co2 gas causes ph to be lower) in it when it comes up but gasses off (as co2 gasses off, the ph rises) after a period of time till it reaches it normal state. mine out of tap is 7.4 and in tank is about 8.2. i'm not sure if this is the answer but its worth a check.

Something about this doesn't quite sit right with me. The CO2 that changes your pH has to be in solution (i.e. not in gaseous form, but dissolved). But, if it gases off, it probably wasn't in solution to begin with (unless the water is supersaturated in CO2, which it isn't). And, even then, the CO2 coming out of solution is going to be neutral (i.e. not affecting the pH); it doesn't leave the water ionized. So, I don't see how the CO2 gassing off could raise the pH. Hmmm .....

Anyways, a pH of 8+ seems pretty high to me. I can see things dropping it, but not raising it like that. I wonder what's going on.

[wondabread]

I have a 36g corner bowfront upstairs in my office using the same tap water and it has no increase in pH.

I also have a co2 bottle on that tank (something that was going to be added to the 75g in the near future) and the pH has dropped to about 6.6.

My tap water is not saturated with co2.

It is either play sand or rocks.

[Pure]

Originally Posted by iapetus

Something about this doesn't quite sit right with me. The CO2 that changes your pH has to be in solution (i.e. not in gaseous form, but dissolved). But, if it gases off, it probably wasn't in solution to begin with (unless the water is supersaturated in CO2, which it isn't). And, even then, the CO2 coming out of solution is going to be neutral (i.e. not affecting the pH); it doesn't leave the water ionized. So, I don't see how the CO2 gassing off could raise the pH. Hmmm .....

CO2 once dissolved in the water lowers PH. If left out it will dissipate out of the water raising it back up. This is a fact. I'm not 100% sure "out-gassing" is the appropriate phrase but it gets the point across.

WB, You have CO2 on that other tank so it can't be used as a control. You need to test your tap water. I do think that something in that tank is causing the PH to raise as much as it is. Play sand should be inert, but then again who knows what they put in it. It could have traces of ground up limestone for all we know. So test your sand too.

But still test your tap water mate.

[emmanuelchavez]

I had play sand in one of my tanks, and there was no pH change until after I started adding CO2. I doubt it's the playsand.
Do you have the API liquid test for ammonia?
One of the bottles should be HCl, the one with the "corrosive" label. Add a drop to your rocks and play sand... you'll definitely know if there's any carbonates in them.

The water makes more sense.

[Whiskers]

-------------------------------------------------------------------------------

"It's possible that your tap water contains a lot of CO2 (most tap water does), and when it off-gasses, your pH raises (since CO2 lowers pH). It could be the type of rocks you're using or something in your substrate. Fill a cup up tonight with tap water, let it sit out overnight, and test it in the morning and see what you get."



I found the post but didn't know how to retrieve Quote so i just copied and pasted it here.

This is what Avalon had suggested to me and how he said it. I don't know enough about some things to know how the tap water gets saturated with co2 but whether or not it gass off or dissapates it still leaves the water causing the ph to change.

[wondabread]

I have a bucket of tap water that I put a few rocks in. I would do one rock per bucket, but I need to figure it out quickly and don't have that many buckets.

I tested the tap water out of the tap. Hopefully 14 hours will be enough to show a change so I can narrow it down to one of the buckets.

I figured sand was inert, after all, I read it on quikrete's website, but wanted to double check with people who have experience.

I almost regretted using play sand after find a pool supply center right next to my petsmart. From pics of other's tanks, the filter sand looks great and has larger particles which makes it easier and better to use.

Once the tank was setup, I didn't regret it. I just wish I had monitored the pH more closely.

BTW - I have several other tanks - a 55g, another 75g, 20L, 20H, 10g, 5.5g, all with water and all but one with fish/animals and no other pH issues like I am having.
Thanks for the all the help!

[iapetus]

Originally Posted by Pure

CO2 once dissolved in the water lowers PH. If left out it will dissipate out of the water raising it back up. This is a fact. I'm not 100% sure "out-gassing" is the appropriate phrase but it gets the point across.

What you say is true. What I should have said is that I don't think CO2 can be responsible for the pH measured here. What I am questioning is whether the dissipation of the CO2 could lower the pH below what it otherwise would be. I am assuming that the tap water wouldn't naturally have a pH of "around 8.4-8.8". The dissolution of CO2 should drop the pH, but it's release can only bring the pH back to where it was before the CO2 dissolved into the water.