Hi everyone,

I was wondering what things can cause pH to rise? Our tank has been set up for about 18 months and over that time the pH has gradually been rising from 7.6 to 7.8 then 8.0 and now 8.2. I am worried about this trend continuing. So what things can affect pH?

Thanks.

Which test kit are you using Katrina? Does the pH from your source/tap water vary? There are many things that affect pH. It may be something you have in your tank that is raising the pH. Sea shells, coral pieces,decorations or stones, limestone ornaments and even sea salt are all rich in carbonates and can over time raise the pH. A gradual raise up is not as dangerous as down and you are still safe at 8.2. The worry is if these fluctuations are also happening the other way round> down= up and down.

It would be helpful to know your tank set up (fish numbers, tank size and contents) and your kH and GH to work out more clearly what is going on.

Hi Trinket,

We have 2 tanks. One is 150cm x 35cm x 27cm, the other is 45cm x35cm x 27cm. The larger tank has 2 orandas, the smaller tank has 2 small lionheads. Each tank has a small amount of gravel at the bottom (bought from pet shop, called coffs harbour gravel fine). The large tank has 2 Eheim filters plus a UV filter & 2 plastic plants. The small tank has 1 aquaone filter, a uv filter, airstone, 1 plastic plant. Each tank was cycled before we added fish. Had the 2 orandas since about May 2006 & 2 little lionheads since January 2007. Ammonia & nitrite = 0 in both tanks, nitrate is < 5 (did a water change yesterday), kh=125.3, gh=214.8, ph= 8-8.2 in big tank and 7.8-8 in little tank. When we first set up the big tank I remember the ph being 7.6-7.8 (so about 1.5 years ago now). The kh & gh I first tested in March this year and they were 89.5 and 143.2 respectively.

Our tap water has a ph of 7.6. Yesterday I tested the big tank water both before and after a water change: before ph=8-8.2 & after it was 7.8. We add the water back in fairly slowly.

Everything in our tank was soaked in tap water then conditioned water for at least a week before we put it in the tank. Everything in the tank has been there for a long time now. Each tank also has a tank light which we've had for maybe 6 months. Where I live, the town water comes from dams which are very low at the moment (we are entering level 6 water restrictions).

We have used aquarium salt a couple of times this year when the fish were sick but have done many water changes since so I doubt much, if any, would remain.

The rise has been quite gradual, I am just concerned about the possibility of it continuing to rise. So am trying to investigate what might cause it.

Thanks!

Just an example of one of the causes:

Increases in pH are usually caused by decor, such as gravel or rocks. Many rocks and gravels sold for freshwater aquaria contain minerals that push the pH and hardness of the water upwards. Even bog standard pea gravel has some minerals that dissolve in your water.
If you don't want your pH to rise, make sure you ask your dealer for decor that is inert. This won't effect the chemistry of your water, so it's safe to use in any aquarium.

From Practical Fishkeeping

I forgot to say that the test kits are API.

How do you tell if the rocks etc are inert?

"Our tap water has a ph of 7.6. Yesterday I tested the big tank water both before and after a water change: before ph=8-8.2 & after it was 7.8."

Had you also tested the tap water before doing the change?

Try this:
Test your tap PH and record it. Then, fill a jug from the tap and let it sit overnight or a little longer - test it the next day. You may discover that the jug PH will have risen. If so, this is because carbonic acid disolved within the water has had time to dissipate, allowing the PH to rise to it's true level. In which case you're real PH is actually 8.0 or so.

If however, the jug PH remains the same, do the following:

Remove anything you wish to 'test' from the tank. Pour a little vinegar over it and see if it fizzes. (Rinse all residue before returning to the tank.
Or, having done the 12/24 hr tap-test, immerse the rock/gravel/whatever and test again after 12/24 hrs.
Let us know your results.

That's a great way to deduce. I'll remember that if I ever have that problem.

Thanks Pixiefish! I didn't know that about pH. I will do the tests over the next few days and post back.