Sudden drop in pH -- not recovering


HI folks,
Our pH levels were steady at 7.2, sometimes dropping to 7.0 briefly , sometimes rising to 7.4 briefly, seemingly with the temperature. Tap water pH is varies from 6.9 to 7.1.

The tank is fully cycled... we haven't seen a trace of either ammonia or nitrites for almost 2 months and are keeping nitrates to below 20ppm and are aiming for 5ppm over time with water changes.

A couple of weeks ago we added some plants (cabomba aka fanwort) and a chunk of wood, both store bought. Immediately the pH dropped to 6.0. It has been slowly going lower since and is now low off the scale (something less than 5).

We removed the wood a few days ago but the pH is still kept dropping. We currently have no way to test for water hardness and from what we've read are advised to not mess too much with this unless there is good reason.

The only LFS we found that is reasonably trustworthy is advising adding some Cycle drops immediately and adding crushed oyster shell. This same person told us to stop the water changes too though so I have my doubts!

Does anyone else have any thoughts? Almost all the pH advice we've found is related to lowering the pH.

By the way, our finned friends are waving hI to everyone. The danios are as rambunctious as ever, the tetras are teasing the danios like always, the cory is ignoring everyone cuz he's got work to do, and the dwarf gourami is counting the minutes 'til the next feeding, pausing once in a while to spit at us in disgust.

Rex Grigg

Any time someone tells you to stop doing water changes just walk away.

The wood most likely is the cause of the dropping pH.

Just do water changes.

Don't add crushed oyster shells or you will find your self with the opposite problem of having high pH and GH and KH.

There is no reading of KH in your post. pH and KH go hand in hand.


Rex gave very good advice. Can't believe they actually said not only to stop doing water changes, but actually thought that the product Cycle would actually effect pH. They obviously have absolutely no idea what they are talking about. The driftwood releases tannins into the water and it is what causes the pH to lower. Did you pre-soak the driftwood before you added it to the tank? If not then it is highly suggested to set it into a bucket fully submersed in dechlorinated water (i.e. use a few drops of your water conditioner to the bucket before adding the wood) and keep an eye on the color of the water. Over time it will most likely start to darken a bit in color (kind of like tea), and this is the tannins leaching from the wood. When the water stains a bit, dump it out and replace it with more dechlorinated water. Keep doing this until the water stops changing color (this could take weeks by the way) for at least a few days. Then it's ready to put back into the tank. As for the tannins that are already in your tank, do 25% water changes for the next few days and you should eventually notice an upward swing in the pH. It sounds like you have fairly soft water for the driftwood to drastically change the pH like that as quickly as it did. To test you need a kit that measures your waters KH level as Rex mentioned... the lower the number the softer your water. Now soft water is not a bad thing per say and can be left alone but understand what it means and what you have to do to deal with it. Basically with soft water, you don't really have a buffer to stop things like pH swings. With a buffer you might have been able to add the driftwood without any pH swing because the buffer actually (if high enough) would absorb all of the tannin's pH lowering ability. If the wood released enough tannins to surpass the buffers abilities you would still get the downward swing, but it might not be as strong since the buffer absorbed most of it. With out that buffer you can still have a happy tank, but you would need to be more careful about introducing anything to your tank without knowing what the effects might be. Also a lot of live plants in a soft water tank might cause pH swings that are rather steep between it's day and night cycles. Plants release oxygen and burn CO2 during the day which raises the pH in your tank, however, at night plants actually burn oxygen and release CO2 which lowers your pH. So a little buffer to curb a bit of that action might not be such a bad thing. If you want to leave things as they are and just see how things pan out (usually a good idea... i.e. cross that bridge when you get to it type thinking) then just keep testing your pH and other qualities of your tank to see if anything gets out of the norm. Messing with the pH can be a tricky thing for even experts to handle so it's not normally recommended, but finding the KH of your tank water and your tap (to be sure they are the same) could be helpful in understanding it you need to dive into that stage of fish keeping or not.


Thank you for your responses...

I've only got a vague grip on the post-grad chemistry involved with pH and am tempted to think the best course is increased water change frequency and hope for the best. My worry though is that pH is so low it is off the scale so I don't know just how badly acidic it is.

The particular individual we talked to at the LFS (over the phone) isn't who we would normally have taken advice from. She usually defers to the other staff who do seem to know what they're talking about. The oyster shell trick is something we see them doing to their own tanks. Of course we aren't going to add Cycle to address pH and of course we aren't going to stop the water changes.

The tank is at best only moderately planted so I don't think that is a cause unless the type of plant is a consideration. Trust me, the wood is not going back in.

We'll add a kh test to our kit and see what that says. Almost out of nitrate test anyway, so I guess a trip across town may be worth it.


Got the hardness kit:
Tap water: GH -40ppm, KH < 10ppm
Tank Water: GH - < 20ppm, KH < 10ppm

Interesting that the pH was so stable for so long when even the tap water is so soft. Now I wonder if there isn't a municipality water issue going on.

Going to let things run their course with all my fingers and toes crossed.


The wood most likely is the cause of the dropping pH.

Yes, it probably is. Although if it was soaked and boiled enough before putting it inside the tank, it should not affect the pH. I have driftwood in 2 tanks and it was boiled and soaked for a long time before it was put in my tanks. It has never had any effect on my water chemistry and pH.
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