Low Ph

[Tessatales]

My 20 long has a Ph that runs between 6 and 6.4, and for the fish I have, that is fine, but I would like to know what could be making it so low. The tank is cycled. No ammonia, no nitrites, between 10 and 20ppm nitrates every time I test. My decorations are slate rock that has been thoroughly cleaned, a fake driftwood decoration, and my substrate is sand. I know that the ph is not coming from the tap water, because not only have I tested it, but I also maintain my 10g with the same water, and its ph is 7.2. My filter is a Marineland Penguin 200b, and my stock is 3 Julii Corys, 7 Harlequin Rasboras, and 1 Threadfin Rainbow (and yes, I am getting him friends, but the LFS only had one in stock!). I can't figure out anything that would make my Ph go as low as it is!

 

[fort384]

It is funny how you can setup multiple tanks with seemingly no differences, and end up with 2, different, stable pHs. How long has the tank been running, and how stable is it?

Are you sure the rocks are slate? Although, even if not, most rock, if it affects pH will have the opposite affect and cause higher pH.

Are you using any filtration meeding in the penguin?

 

[Tessatales]

It is funny how you can setup multiple tanks with seemingly no differences, and end up with 2, different, stable pHs. How long has the tank been running, and how stable is it?

Are you sure the rocks are slate? Although, even if not, most rock, if it affects pH will have the opposite affect and cause higher pH.

Are you using any filtration meeding in the penguin?

The tank has been up for about 2.5 months. I used established media when I started it, and I haven't taken out all of the media yet. It has a few biowheels and some old filter floss from an established 55 (which has a normal Ph). I also have a bag of ceramic rings in the back of the filter to give the filter a little extra surface area.

The rock is definitely plain slate. I actually just added a rock that is slightly alkaline to see if it would bring the ph up a little, so I will see how that works out.