Old saltwater tank causing high PH? - The Planted Tank Forum
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post #1 of 3 (permalink) Old 02-14-2014, 03:39 PM Thread Starter
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Old saltwater tank causing high PH?

Hey, first time poster here, new to the forum and to planted tanks. Which brings me to my question-
I just broke down my 55g saltwater tank to make it a FW planted tank. I rinsed the tank and filter with hot water, changed all the filter media (fluval 306 cannister) and just generally tried to remove any old scum and leftover salt creep. Right now the tank has a couple big peices of driftwood, some river rocks and a fluorite base with play sand over top, and is filled with freshwater. No fish or plants yet, it has been set up and running for about 2 weeks.
The tank ph is 7.4, but the ph of my tap water is very low, like close to 6.0. Could the ph be high from some residual salt left in the tank or the filter? I really didn't think that some leftover salt residue would have that much of an affect on 55 gallons of freshwater.
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post #2 of 3 (permalink) Old 02-14-2014, 08:12 PM
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It sure shouldn't. I had a 125 gallon salt water tank that I used for fresh water after thorough cleaning and there was no issue at all.

Look into the play sand. It might be a limestone based sand, and the minerals in the sand could be contributing to the GH, KH and pH.

Test a handful of the sand in a separate jar of tap water. Test GH, KH, pH and TDS when you start and every few days for a week or two.

Do the same test on rocks or other things in the tank.

pH is not a stand-alone value. It is affected by other things in the water.
If the KH is fairly high then the pH tends to be high, and stable.
If the KH is low then the pH can vary quite a bit, depending on what else is in the tank.
Generally organic matter and organic processes such as decomposing fish waste, fallen food, old leaves and so on create an acidic reaction. Adding CO2 usually makes an aquarium more acidic, but in a daily cycle as the plants use varies night and day.
Carbonates and bicarbonates in certain fertilizers will add to the KH and this generally makes the pH rise.

The link between KH and pH is not a hard and fast rule, but a pretty decent guide as the first thing I would check to see what is going on with the pH.

If you can post GH, KH and TDS levels of tap water and tank water that might help us to figure out what is going on.
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post #3 of 3 (permalink) Old 02-14-2014, 10:40 PM
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Originally Posted by Hickorylarge View Post
The tank ph is 7.4, but the ph of my tap water is very low, like close to 6.0.
You probably just have CO2 in your tap water..which is very common....aerate it first in a bucket
CO2 is acidic, so it lowers the pH

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