pH higher than usual in blackwater tanks.

[echoofformless]

I don't test my water often but whenever I do it's always well below neutral in my blackwater tanks. Tons of wood and peat filtration do a good job in keeping things nice and acidic.

But today i tested just before my fortnightly water change and both tanks came out to be around 7.2-7.4!

This doesn't make sense for several reasons:

1. My source water is from the tap and tests at neutral both straight out and after a few days aging.

2. I run lots of peat in my filters and have loads of wood in the tanks.

3. The tanks are long cycled and the nitrification process should be making the tank more acidic just by default.

4. I've nothing in the tanks that would raise the KH or GH much less the pH. No calcified rocks. No additives or buffers. The tanks are quite au naturel.


What's the deal??

 

[Mgamer20o0]

what was the ph? when was the last time you tested your water? lsat time you changed your peat?

 

[echoofformless]

the water always used to test approximately 6.4 - 6.8 and i'd say the last time i tested it was around three weeks ago. i test the two blackwater tanks the same day since they get tandem water changes.

and as i said tap water always tests around 7. philadelphia has a fairly good water department so sudden changes are rare if ever. and being as though my tank water has always shown the acidifying effects of the peat, wood and nitrification i can't assume that the tap water has caused the change.

as far as changing peat i usually do that about once a month. that's the same frequency i've kept for almost four years. so i can't really attribute it to the peat getting weak.

and still even if the peat got weak, what would cause a tank to go alkaline without any base there to make it do so? i always assumed that tanks get acidic over time and not the other way around!

it is funny though. i'm having a good laugh.

 

[TwoTankAmin]

Three things occur to me. First is it possible that the kh of your tap has gone higher? this would make changes in pH harder to do.

Second, the wood leeches tanins, but they are not limitless. Over time the tanins leech out of the wood til they are depleted.

Third, peat in a filter is notoriously unreliable for pH changing. It is uncontrolled and may effect the water faster or slower. Many suggest pretreating the changing water with the peat rather than doing it via a filter.

Peat moss softens water and reduces its hardness (GH). The most effective way to soften water via peat is to aerate water for 1-2 weeks in a bucket containing peat moss. For example, get a (plastic) bucket of the appropriate size. Then, get a large quantity of peat (a gallon or more), boil it (so that it sinks), stuff it in a pillow case, and place it in the water bucket. Use an air pump to aerate it. In 1-2 weeks, the water will be softer and more acidic. Use this aged water when making partial water changes on your tank.

Peat can be bought at pet shops, but it is expensive. It is much more cost-effective to buy it in bulk at a local gardening shop. Read labels carefully! You don't want to use peat containing fertilizers or other additives.

Although some folks place peat in the filters of their tanks, the technique has a number of drawbacks. First, peat clogs easily, so adding peat isn't always effective. Second, peat can be messy and may cloud the water in your tank. Third, the exact quantity of peat needed to effectively soften your water is difficult to estimate. Using the wrong amount results in the wrong water chemistry. Finally, when doing water changes, your tank's chemistry changes when new water is added (it has the wrong properties). Over the next few days, the chemistry changes as the peat takes effect. Using aged water helps ensure that the chemistry of your tank doesn't fluctuate while doing water changes.

From http://fins.actwin.com/aquariafaq.html

 

[echoofformless]

The hardness of my tap water is pretty consistent. According to my tests and also the water quality report, Philadelphia's tap water averages about 3.5 dkh / 63ppm. My non-hard water tanks all test at about this level as well. And my blackwater tanks test at slightly below this - between 2.5 and 3 dkh. (Around 43 ppm.)

And even if the tap water had gone higher, I haven't touched the water in the tanks for two weeks. And from what little I know about aquarium water chemistry, tanks will naturally go acidic without the addition of alkaline buffers. So that means that even if the peat is spent and the wood has leached its very last tannin there still shouldn't be any increase in pH without me having added something to the system to make it so.

And finally I've been using the peat in this way for the better part of four years. It always has a good consistent and mild effect on the hardness and the pH. I don't see the peat itself being an issue.


None of this is making scientific sense to me. I gather that the only explanation is that there is a buffing agent somewhere and I can't for the life of me figure out what it is.