pH Creeps Up

I have a question about pH. My tap water is pretty high in pH, GH, and KH. So I have been using a mixture of spring water and distilled water (eventually I would like to get an RO/DI filter). The water I add to the aquarium is pH 7.4, GH 3 deg, and KH 4 deg. My aquarium measures pH 7.4, GH 4, and KH 4 after water changes. I also have a CO2 diffuser, which I fill up once per day, which can drop the water to pH 7.2, but by morning the pH will be returned to pH 7.4. Both the GH and KH remain pretty constant, but the pH will also creep up higher as the week goes on. So, it went from pH 7.4 to pH 7.6 in about 4 days time. I know that KH bufffers the pH, but my KH is low. I read something that said that phosphates can possibly cause a buffering, so I measured my phosphates and they are low - between 0 and 0.24ppm. So I am wondering if there is something else that can be buffering my water that causes my pH to raise higher over time? I use the Eco Complete substrate, and I was wondering if that could be having an effect? I cannot understand why my pH does not stay more stable! Does anyone have an explaination for this?

Thanks

 

When you say your tap water is high PH, how high is high?

The PH readings out of the bottle are not the true PH of the water. To get the true PH of your distilled/bottle water concoction, pour some in a bucket with an airstone running for a couple of days and then measure your PH.

I ran this experiment with bottled water and the PH increased from 6.8 to 7.2 in two days while the GH and KH remained constant.

I'm using a 50/50 mix of sand and eco-complete and have not experienced any PH fluctuations.

 

The tap water is pH 8.1, GH 15 deg, KH 11 deg.

I will have to buy an airstone and pump to do your experiment on the bottled water. It may be worth it as I am not able to explain why this would happen. I do have some water premixed, that I keep at room temperature, without the airstone, that might tell me something. How does the airstone make the pH adjust?

 

hmm, sounds exactly like my tap water. If it were me I would just use my tap. Having a stable PH is more important than a "proper" PH. Plus, if you were to have a situation were you needed to daily water changes, your process could get expensive/irritating. Just my 2 cents worth.

If you have premixed water that's been sitting for a few days then go ahead and test it. Honestly, I've also done the experiment without the airstone and have seen the PH shift.

The airstone aggitates the water surface causing a gas exchange > O2 into the water and CO2 out of the water. As CO2 decreases, PH increases. Check the link ->

 

Also, this sticky at the top of the PH forum has some great info.

https://www.fishlore.com/aquariumfishforum/threads/ph-gh-and-kh.114872/

 

Thanks, 2HeadedBoy. I will look into this further. But this would also mean that my tap water is probably higher than pH 8.1 as well. I will have to perform the same test to both water sources.

The link to that chart is very interesting. It shows me the correlation between CO2 levels and pH. So I am surmising from this that as my plants produce O2, and use up CO2, my tank pH will continue to rise. Using the CO2 injector replaces some of the CO2 taken up by the plants, and then slightly draws down the pH. Then the tank pH will cycle as C02 is used and replaced. - And, as you said, the source water needs to be oxygenated (as it would be in a well planted tank I would assume), to find out what the pH would after a few days in the tank.

 

There is a dellicate balance between plants, lighting and CO2/nutrients. A balance that I am nowhere near mastering yet.

As you are aware, plants use CO2 and produce O2 during photosythesis which occurs when the lights are on. When the lights are off, this reaction is greatly reduced. This may result in PH fluctuations depnding on what time of the day you test. However, I think the tank needs to be pretty heavily planted for PH shifts to occur though.

Also keep in mind that if your tank PH is a natural 7.6, then doing a normal weekly 20% water change with 7.2 water will not affect the overall PH of the tank very much. If you were concerned, you could always prepare the water needed for the change a couple of days ahead so that it's PH adjusts before adding it to the tank.

If it were me I would start doing PH tests on the tank water every 1-2 days. Do this at about the same time every day. You may find that even though the water you're adding is 7.2, the tank water stays at a stable 7.6. And having a stable PH is what is important.