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Hey everyone!

I was cleaning a few of my tanks and doing water changes today, and decided to test parameters too (I do this about once a month). My longest running tank is a lovely planted 12 g, well established, a month shy of two years old. I was surprised to find the pH way down, 6.4, maybe lower, when normally it's closer to 7.4. This has happened a couple of times previously, with no negative results, and I add some crushed coral to bring the pH back up. But I was wondering why this happens. I feel like I know the answer, or should know, but wanted to ask here and see what others had to say on the subject, and also if it's something I need to concern myself with.

Thanks in advance!

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Did you originally have crushed coral in the tanks/filters? Its possible.it has been used up over time- the stuff that dissolved easily has been used and now only the harder to dissolve portion is left (I recall Cory mentioning this in one of his videos.) Adding more crushed coral- as you have already done- is a good solution.

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I have not added anything like driftwood since the tank's inception 23 mths ago. The crushed coral is only added (in a small sac and placed in the HOB) when I discover this, and once the pH goes up, I remove it. This has happened about every 6 mths. It's not a problem, per se, but I'm curious as to whether it is indicative of something else, if it could actually BE a problem, and if it's something I should be addressing so it doesn't occur again. I can safely say I have never had a problem with ammonia in any of my tanks. Sometimes my nitrates get a bit high, but that's the only other "issue" I could mention. 

Ben Ellison, can you please explain what my water hardness (2-3) has to do with my pH lowering over time? I do water changes approx every 1-2 weeks, but I don't TEST that often, only about once a month, or every couple of months. 

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In a planted aquarium pH tends to drift down as organic acids build up over time. Water changes can bring the pH back up because this dilutes the organics acids.

It doesn't sound like you are having any problem with your water chemistry. I assume your fish are healthy and you are otherwise happy with the tank.

pH also varies over the course of the day, so it depends on when you measure it. As you can see from last week in one my aquariums the pH is lowest in the early morning everyday. This is because during nighttime photosynthesis runs in reverse and plants take in oxygen and give off carbon dioxide with the peak build up of CO2 being in the early morning thereby lowering the pH. Once the lights are on (or the sun is up in the case of the graph below) plants begin to photosynthesize and thus begin to consume carbon dioxide and release O2 again. As you can see below, my lowest pH occurs at 8 am in the morning and the highest pH occurs at 4 pm in the afternoon just like clockwork.


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Daniel, this is brilliant, thank you! I am indeed very happy with the tank, and have not suffered any losses of my happy and healthy fish and snails. Just as an fyi, I do not do huge water changes in this tank as a rule, due to the snails. The most I do is 25%. In looking at your pH levels, I see they are quite low as well (to my eyes) and you do not seem concerned. I am wondering if I should be concerned, if I NEED to increase my pH, or if I should leave things alone. What do you think?

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My general theory of life is leave things alone, although I am very inconsistent and violate this all the time.

For me, if the pH is above 6 then I am okay. A better indicator than a test is plant and fish health. If they seem healthy, then they probably are and you shouldn't worry.

Both routes have risks. Not paying attention as your aquarium deteriorates is risky, but often I see on this forum too much concern with an easy to measure number and the vicious cycle people get into trying to push those numbers around. You can lose track of the big picture.

A couple of caveats, I do relatively frequent water changes using aged water, usually at least once a week, occasionally twice a week. Why? I like doing water changes, most people don't. Because the changes are frequent the new water is very similar to the old water so I may not be changing my water chemistry much (which is often the whole point of a water change, that is you are trying to improve your water chemistry), but the flip side of that is my water chemistry never changes very much which is also a good thing in its own right.

Plants like it better when the pH is somewhere on either side of neutral, so if it goes down too low your plants may not grow as well.

But since many of my plants like hornwort, bacopa, ludwigia, banana plants, etc. were wild collected in acidic, tea colored ditch water they don't care if the pH is a bit on the low end.

All biology has way too many variables and what works for me, might not work for you. I am probably not aware of many of the things I do because they are just habits that have built up over the years.

All in all there is a lot to be said for if it ain't broke, don't fix it. The key is to know when it is broken. Go with you gut on your aquarium, if what you have been doing has worked, keep doing that.


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