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517 Posts
Discussion Starter · #1 ·
Hi everybody! Wondering if someone can give me some quick help.
My tank specs, approximate values:

9 Gallons
~2wpg 50/50 lighting, yes it does grow plants and I do think it looks pretty :)
Inert sand substrate obtained from a good LFS
HOB filter (up to 20gal)
Elite single sponge filter also
NO co2
6.6 pH
0 Ammonia, Nitrites
~10 to 20 Nitrates
no current idea what kH and gH or anything else is.
Fishies: Cherry Barbs, Ottos, Cory Cats, Ghost Shrimp, Snails
Plants: Anubias, Java Ferns & Windelov, Water Sprite, Hygrophila Corymbosa & Angustiifolia (or narrow leaf? whichever), Naja Grass, Redroot floaters,
Once a month 50% water change. Top offs when needed.

So it's been set up for months now and I don't use any funny chemicals or additives, maybe random squirts of excel for the hell of it. So my confusion is, why is the pH only 6.6? My nonstagnant empty 55gallon tank is 7.6 pH, and my newly set up barely planted 2.5gallon tank is also 7.6 pH with everyother day 25% water changes. Only co2 I have is DIY on my 5.5gallon aquasoil planted tank, which with co2 is 6.4-6.6 pH. So what gives? Are the plants I have in the 9gallon lowering the pH?

Here's an old picture of it when it was set up all those months ago, missing some plants I listed.

Can anyone offer any possible reasons my pH is so low? I don't have the pH out water out of the tap but I assume it's 7.6 because my empty tank hasn't been disturbed for months. Thanks in advance


1,600 Posts
A couple thoughts come to mind. First, yes, certain plants will lower pH. There are certain plants (most notably Vals from what I recall reading) that will strip out carbonates (part of KH) if they can't find CO2 in the water, and thus over time, it will reduce your CO2 levels.

Second, CO2 is a pretty funky thing. My KH ~8, and my main CO2-fed tank has to be down around pH 6.3 for me to get any pearling. Clearly, the "classic" CO2/pH/KH charts don't apply in my setup, because otherwise there would likely be fish deaths.

Third, I've had "toxic" driftwood which was leaching heavy amounts of acids (not 'visible') and completely chewing through all the KH *and* GH in my tank. This seems to be fairly rare, as I've not seen many other reports of it. But, it certainly could be something particular to the tank that is 'attacking' the KH levels.

It would be interesting to see if your recently setup 2.5g tank exhibits the same 'behavior'.

842 Posts
$100 says your plants have nothing to do with it.

Maybe the rocks? It may also be naturally occurring humic acids that are the result of decomposing organic matter (fish food, dead plant matter etc). I have noticed that all of my tanks tend to get more acidic over time.

BSS- The CO2 chart only works when carbonate is the only buffer present in the water, That's why people use drop checkers with a known KH made from distilled water. We have all kinds of other compounds in our tanks that will effect the Ph, like tannins from driftwood, phosphates and others.
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