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Old 03-13-2011, 05:32 AM   #1 (permalink)
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Default Why does my pH always rise?

My tap water is very basic. But, even when I treat the water, within a few days it rises back up. Does anyone know why this is happening? Also, are there any inexpensive ways for me to keep my tank at a low pH?
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Old 03-13-2011, 07:35 AM   #2 (permalink)
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Default Re: Why does my pH always rise?

Need a little more info. Do you use a bubble wand or an HOB filter?
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Old 03-13-2011, 08:07 AM   #3 (permalink)
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Default Re: Why does my pH always rise?

I have a hang-on filter and heater. No co2 tank or anything like that. The scape is driftwood, the substrate is aquasoil amazonian with a layer of mineralized soil underneath. The tank is moderately planted (not dense, but not sparse either)
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Old 03-13-2011, 09:53 AM   #4 (permalink)
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Default Re: Why does my pH always rise?

When plants use up the co2 , PH rises.
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Old 03-13-2011, 10:08 AM   #5 (permalink)
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Default Re: Why does my pH always rise?

could be your water district adds co2 to you water.
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Old 03-13-2011, 10:52 AM   #6 (permalink)
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Default Re: Why does my pH always rise?

New tank? Either way there are a few things to do to figure out what is happening. 1. Test the pH of your fresh tap water. 2. Put some fresh tap water in a cup or jar with nothing else in it. 3. Put some more tap water in a jar with some of your substrate. 4. Test the pH in 2 and 3 after a few days, and maybe again after a week.

The pH of water will change with the amount of CO2 in the water, so if your tap water has a high amount of CO2 in it, the pH may seem to change all by itself. Also, your substrate may tend to make the water either more alkaline or more acid. If you have shells, coral, limestone, etc. your pH will tend to rise over time. If you have wood or peat, it may tend to go down. Treating the tap water is not likely to overcome these other influences for very long. If you want a low pH tank, you need to make sure you have no tank substrate or decorations that are raising the pH, you can add a bag of peat to the filter media (this will darken the water as well as lower the pH) or you can start out with RO water and carefully add back what you need. It can be a lot of work. Many municipal water systems add carbonates to the water supply to raise the pH as acidic water can leach lead or copper out of old pipes and cause problems. Overcoming these buffering agents is not always easy. Also, ammonia raises pH - do you have adequate filtration?

I highly recommend choosing fish that are happy with the chemistry of your tap water (except for chlorine and chloramines). If you have your heart set on something that isn't, be prepared for a lot more work, choose your tank decor and substrate very carefully, and use a container (like a clean trash can) to age and treat water for water changes.
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Old 03-13-2011, 04:55 PM   #7 (permalink)
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Default Re: Why does my pH always rise?

Quote:
My tap water is very basic. But, even when I treat the water, within a few days it rises back up.
'Very Basic'
Probably has high carbonate, measured by the KH test.
Carbonate is a buffer that tends to stabilize the pH in the higher range, often in the upper 7s into the 8s.

When you add acid the pH drops temporarily, then the buffer takes control of the H+ from the acid, and the pH rises again.

To make a permanent drop in the pH do this:

Set the GH and KH where you want (perhaps about 3-5 German degrees of hardness) by mixing reverse osmosis water and tap water.
Then add some peat moss.
Specific method:
Start by buying a gallon of RO or distilled water from the grocery store. Mix perhaps 1 quart of it with some tap water (a cup or 2? A pint or a quart?) you will have to test and find out the right ratio) until the GH and KH read 3-5 degrees.
You will have perhaps 1-2 quarts of mixed water.
Put about 1/4 cup of peat moss in there. It is OK loose for this test. If this works for you, you will put the peat moss in a nylon stoking in the filter.

Test the GH, KH and pH daily or every few days for a week or two. For the first day the pH should drop as the peat moss works, then things should be stable, or may continue to drop slowly.

Note:
Most hatchery raised fish even if they came from soft water are usually fine in harder water unless you are breeding them.
Wild caught fish or their descendants that have only been ever raised in soft water will need soft water. Cardinal Tetras, for example still get calcium deposits in hard water.

Note I keep saying SOFT water, not low pH. These fish are looking for low GH, KH and TDS (Total Dissolved Solids), pH is much less important.
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Old 03-13-2011, 06:27 PM   #8 (permalink)
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Default Re: Why does my pH always rise?

Have you tested your tank for ammonia build up?

Substrate causing it?

Tap water has additives to lower pH and these can dissipate once out of the supply system and the pH will rise again. Basic water tells me it normally has a high pH and your additives dissipate.

Add peat to the filter.
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Old 03-14-2011, 05:32 AM   #9 (permalink)
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Default Re: Why does my pH always rise?

Tap water usually has additives or treatments that do a couple of different things.
If there are high mineral levels in the source water one goal of treatment is to soften the water. This is not always done, though.
If the water tends to be neutral or more acidic (lower pH), the other treatment is to make the water more alkaline, higher pH, since low pH is harder on the distribution pipes.

If there is high carbonate levels from the source the water will likely test "basic" or "alkaline". The pH will be over 7.0, and resistant to change.

If the water company adds something that is not carbonate or bicarbonate to make the water more alkaline then the pH may be high, but the KH will not be so high. This is typical of my tap water. GH and KH are around 4-5 degrees, but the pH is in the upper 7s, occasionally low 8s because of sodium hydroxide added by the water company. The pH of my tap water is pretty easy to alter with peat moss or pH additives because the carbonates that might buffer it are not really very high.

If the water is high in any buffer then the pH will be resistant to change. The OP posts that it is resistant to change, and resets to the higher pH that comes from the tap. This suggests a buffer that buffers in the upper 7s or so. Carbonate is one of the more common ingredients that meets this criteria.

It is not the only thing, and without a few more tests or a phone call to the water company we probably won't find out what is done to the water.

However, diluting tap water with RO or distilled water will dilute whatever is in it, and may make the pH more amenable to change.

I would like to see test reports from the OP or a link to the water company's annual report (often these are available on line) to get a better feel for what the tap water is like, and to see the test results of the blend of tap + RO with and without peat moss.

Often tap water will have gases dissolved in it. If it is high in CO2 then the water out of the tap will have a low pH that rises when the water sits out for several hours or overnight. Other gases may show up as cloudy water that clears really fast. These are tiny bubbles.

Best tests for these:
Tap water: Run the tap for a minute or so to get rid of water that may have been standing in the pipes.
Run a glass of water.
Look for cloudiness. See how long it takes to clear.
Test for GH, KH, pH and TDS.
Allow the water to stand for 24-48 hours and repeat the pH test.

Test the tank for all these, too.

GH: tests calcium and magnesium.
KH: tests carbonates.
pH: tests pH
TDS: tests Total Dissolved Solids.
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