Are My Plants Raising My Ph?

[Griz]

I'm have trouble lowering the pH in my tank and wondering if the plants are raising my pH despite my attempts to lower it. The reason for all of this is that I really would like to keep some more Apistogramma and having a lower pH/GH/KH/ will allow me to get some species that I can't keep successfully with 7.8 Here's the situation:

It's the 33 gal in my sig which I would call moderately planted. Two big sword plants, a fair sized clump of crypt wendtii and several bunches of java fern. The tank has been running for 3 years. My tap water is pH 7.8, GH 9, KH 4. I used Fluval peat pellets in the filter for 2 years and more recently have used blackwater extract. I have 7 pieces of fair sized wood. The fish and I like the tannins but there has been no effect on pH or hardness.

With the fish I have, I've always wanted a slightly lower to pH. With a KH of 4, I would have thought that I could move my pH and hardness at least somewhat. I was mesing around with peat, wood and blackwater extract and found I was easily able to lower these values in a test tank. I then read about plants raising the pH and had an AHA!! moment.

I'd like to hear what you think and also what are your opinions on using CO2 to raise pH in this tank. I have rather low light (20W) but lots of natural indirect light in the room.

 

[George Farmer]

CO2 injection would lower the pH for you, and benefit your plants. I won't change your hardness though.

Peat has a limited effect on hardness, it doesn't budge GH and may only temporarily lower KH (and therefore pH).

Mixing RO with your tap is a very effective way to soften water.

 

[Griz]

Thank you George.

I may try DIY CO2 in a test tank I have set up. I really hesitate to mess around with my main tank. Everything is very stable, however if I am to get the apistos I want I really need to lower the pH from 7.8 to about 7.2 and keep it stable.

I don't understand why I can't seem to lower the pH using the methods I've tried above. Do you think that my water is too hard to lower pH this way? Do you think that it's the plants that are preventing this? If the plants are the cause, I may set up a seperate apisto tank without plants. The test tank has been going for 4 days now and using 3 cups of peat in 15 gallons I have the following: pH 7.0 / GH 4 / KH 2. Time will tell how stable this is, but it it makes me wonder why I can't achive the same results in my main tank. Any ideas?