PH crashing up?

["Alan Whitten" <caw18 at bak_rr.com>]

I posted this to the Apistrogramma list, and it was suggested that I post it to this list.  So here the question:

Ok, Ive got a wierd one here...

I have a couple of nearly identical 10 gallon tanks.  Each tank has a substrate of about 75% silica sand, and 25% coated aquarium gravel.  Under the aquarium gravel, I have placed about 3 cups of Flora Base, a commercialy avalible substrate.  Planted in the substrate is an assortment of Amazon swords, and other plants.  Each tank also has a floating matt of algea, and java moss.  The tank is lit by a couple of 4' strip lights that light all four tanks on that level.

The tanks are filtered by identical air driven foam filter.

Each tank contains a chinese algea eater, and either 5 black neons, or a couple of Zebra Dainos (sp?).  The fish are just there as dithering fish for future Apistrogrammas.

The water I am using is a mixture of RO water, and tap water.  I add a little baking soda, Kent's RO right, and some Kent's PH control Minus.  After mixing for about 24 hours, my change out water has a Ph of around 6.5, A GH of 2, and KH of 2.

What is happening is this:  I add my mixed water, and the PH drops down to around 7.  Within 24 hours it will rise up to around 8.4!  I tested the KH, and it is still at 2 or less in some cases.  So what is driving the PH up?

I have ruled out the gravel and the sand, and I hope to test the flower pots soon.  But I would think that anything that drives the ph up would also effect the KH.  It should be noted that my bare bottom tank that gets nearly daily water changes with pure RO does not do this.  It has a fairly constant PH of 6.8.

--C. Alan



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