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Re: Why is my freshwater tank always very acidic?

> From: "me" <tyneside at singnet_com.sg>
> Subject: Why is my freshwater tank always very acidic?
> I have a 3 ft Discus community tank, runs on UGF with 30 watts plant
> fluorescent lighting. Substrate is just normal sand. The tank is only
> half-filled because of leakage near the top, so I estimate that the total
> vol of water is 72 L. The problem is that no matter how much water change
> I've done, its always very acidic. My PH test kit can only measure down to
> 5.0, but I guess my water is even lower than that. I've done 75% water
> change in a period of 2 weeks but the PH never goes up. My tapwater is
> slightly alkaline with a PH of 8.0. I have very few plants, about a dozen of
> baby parviflorus sword and some common stem plants with no CO2. However,
> there are about 3 large pieces of driftwood. 1 of which is about 10 yrs old
> which frequently produces white fungus-like hair on it. So, I'm suspecting
> that the driftwood is the cause of the high acidity. But my fishes have no
> problem with that. However, plants are not doing well though. Advice pls.

First question, what's your alkalinity? I'd bet that's your problem. 

Eventhough your tap water has a pH of 8.0, it may not have any 
appreciable alkalinity, which is your buffering capacity. Our tap 
water alk is 0.5 dK (~9-10 mg/L). Our water report says they add 
NaOH to get the pH up (bastards!), but if you let it stay as is in a 
tank for a while, the pH will bottom out at ~4.5, because of natural 
nitrification. I add 1/4 tsp baking soda per 3 gallons to get a 4-5 dK. 
With CO2, the pH stays a stable 6.8-7.0.

Try testing the alk before going any further.

Jamie    <"\\\><  Aquatic plants, water chemistry, and cichlids