Trying to figure out why the pH in my tank keeps lowering?

[lordhans]

Sorry for the text wall, just want to provide as much information as possible because I can't figure this out:

On my liquid API test kit the pH color for 6.0 (or presumably less) is yellow. This is the color I get when testing the water in my aquarium. When I use the 'high pH' test kit I also get yellow, so I don't think it is actually really high and just registering yellow with the normal pH test kit. I cross-checked the results using a API pH test strip and also got 6.0.

I have a 100 gallon tank that has been in operation for a few years. I recently started to get into the hobby and am trying to learn about how to provide a good environment for my fish. In checking the tank's water conditions I am getting low pH readings of 6.0 (or possibly lower, the API test kit only reads down to 6.0). I checked my tap water and the pH is in the 7.8-8.0 range-- so its much higher than that of the aquarium. I have done probably 10+ 10-50% water changes in the last 2 months because of a high nitrate level concentration I was having. Because of this I would expect the pH of the tank to be higher, as its being infused with so much high pH tap water. But for some reason the pH seems to lower in the tank very quickly. For example, I did a 20% water change a few days ago and the tank's pH went up to 6.6 but when I checked the pH today it is down to the 6.0 (or lower) reading. 30 Hours ago I did a 40% water change and the tank pH came up to 6.8, but now it is back to ~6.0.

Note that high nitrate levels are no longer a problem and they have been under 40ppm for over a month and several water changes.

I have tried leaving the tap water in a glass for a few days and it remains at a high pH level.

Over the last week I have been using some RO water with a pH 7.0 I got from a LFS. This has accounted for 1/2-1/4 of the water I am using during the changes.

My tank is currently stocked with:
-~Inch think of gravel/rocks on the bottom--typical aquarium stuff that has been in use in various aquariums 10+ years.
-Two pieces of small-medium driftwood that have been in use in various aquariums 10+ years. I also had a large piece of driftwood which is only a few weeks old in the aquarium but I removed it as I read the tannic acid that leeches out can lower pH levels (although I had soaked it for 2 weeks prior like recommended).
-A glazed ceramic 'log' thing.
-A few small granite rocks.
-Several fake plants.
-Two real plants (a Amazon sword and some elodea)
-Two filters (one is a back hanging filter and one is a canister filter with carbon, de*nitrate, and those ceramic things for bacteria to grow on, as its filter media).

Thanks for any help/ideas/suggestions!

*Edit for formatting

 

[jsoong]

Hi & welcome to AA!

I gather your tap water has pH of 7.8, which remains stable when sitting out on its own, but when use in your tank, the pH drops to less than 6.0.

There are 2 possibilities:
1. The water has a volatile base. If the water had been limed (ie Ca(OH)2 or CaO added to artificially raise the pH - the water co do this to prevent pipe corrosion), the Ca(OH)2 reacts with CO2 in air, and the pH will fall. In this case you should see the pH fall with the tap water sitting out, but it is possible the fall is not enough for you to notice, esp. if the water is not well aerated while sitting (the change will be small).
2. Something in the tank is removing the base buffer in the water. There is nothing in your list that suggests this. With a 100 gal, a couple pieces of drift wood will not do this. People who wants to drop the pH need something like 1 gal of peat per 5 gal of water.... Also, granite should raise the pH....

Knowing the KH of the water is helpful. If the tap water has a volatile base, then KH would be low. If the tap water has high KH, and your tank KH is low, then something is consuming your buffer. <Note that RO water has no KH, so you are diluting the KH with your 25% RO, so you would expect the tank KH to be lower than tap, but at pH of 6.0, I would expect the KH to be unmeasurable.>

 

[lordhans]

Thank you for your welcome.

So should I try buying a KH test kit as a first measure?

 

[jsoong]

Get your own kit, or get the lfs to test the KH for you. <As a rule, you only do KH once or twice to know your water chemistry, so a whole kit can be wasteful.> Also, if your water co. post water info on-line, get that. You can figure out the KH from the water analysis, and also if they have added lime or otherwise doctored the tap water.

Unless you are adding CO2 for your plants, in that case, you need the KH kit.

 

[beagle]

My tank acts similar. PH is 6.8-7 out of the tap but tank was 6 or below.What solved it for me was adding some crushed coral. With the crushed coral added my pH stays around 6.8. My tap water is really soft and has no buffering capability.

 

[lordhans]

I ordered some crushed coral.

I was planning on putting it in a media bag and then putting it in my canister filter.

How much should I add at a time? And how long should I wait to see what effects it is having before I consider adding more?

Thanks.

 

[eco23]

Scroll down a bit in the same section you're in now, and you'll see a thread called something like "pH 6.0 due to heat". We actually just talked about CC and how to add it. It'll save me some typing

 

[lordhans]

Thanks!

For reference here is the link:

http://www.aquariumadvice.com/forums/f12/ph-below-6-0-due-to-heat-162790.html

 

[sobersteve323]

Scroll down a bit in the same section you're in now, and you'll see a thread called something like "pH 6.0 due to heat". We actually just talked about CC and how to add it. It'll save me some typing

I think you should type it again!

 

[eco23]

I think you should type it again!

One you get over 4,000 posts...linking things and suggesting stickys becomes more and more of an enjoyable option, lol.

 

[chagoi]

Alkalinity (KH) is important. Yes get a test kit in fact get a test kit for all water parameters. If you think of it as keeping water that fish happen to be in your fish will be happy. Baking soda will bring PH & KH.

 

[lordhans]

OK, I will pick up for KH test kit.

In the mean time I did a 20% water change and added about a handful of crushed coral (in a media bag put inside of one of the filters).

The pH measured 7.0 right after the water change. Over the last 3 days the pH has been slowly dropping--about 0.2 a day. It is not ~6.4.

So, the pH is lowering but seems to be doing so at a slower rate. Before, the pH would be back down to 6.0 or less within 2 days.

Should I add more crushed coral? Or wait a few more days and monitor the tank pH? Also, if/when I add more about how much should I add at a time? I don't want to over do it.

Thanks.

 

[jsoong]

You can't overdo crushed coral. Basically, it will dissolve in until it reached equilibrium (and no more), and keep the pH there. So people just add a lot, and leave it in the tank. It will dissolve in as needed, and is more or less set & forget. <You need to replace the cc as it will get used up .... if you have an acid source that is using up the buffer, and it appears you do, you might have to replenish it fairly often. Once you doctored your water, it is no longer safe to do large pwc with plain tap. Around 10% is OK, but anything more, and you should match the KH in the change water. You can either soak cc in your change water for a few days, or in a pinch, add an appropriate amount of baking soda.>

Checking the KH (tap & tank) is still a good idea, since you really want to know what you are dealing with before doctoring the water.