Gravel raising pH? - The Planted Tank Forum
 
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post #1 of 4 (permalink) Old 08-14-2012, 03:12 AM Thread Starter
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Gravel raising pH?

I always thought that pea gravel was inert, but after reading this article it appears as if though that is not the case, and that standard pea gravel has enough calcium to boost pH and water hardness. This is of concern to me because I keep softwater species such as cardinal tetras and otos.

I've tested the pH of both the tank water and tap water using a liquid test kit (only option I have), and they appear to be around the same, with the tank water possibly being slightly more basic. Both are between 7.2 and 7.6 (around 7.4), and if there is any difference in pH it is very small. Is the small difference due to an insignificant amount of calcium in the gravel, or due to the age of the gravel, meaning that any pH boosts would have occurred already? Or could it be from other factors, such as decaying plant matter or the many vals I have in the tank using carbonates from the water? Also, the test was conducted an hour or two after the lights had turned off.

I have two types of gravel in the tank. The first type is white and brown pea gravel I put in the tank when it was first set up in 2003. The second is some Petco brand black gravel, which appears to be colored with the actual gravel being white. The black gravel was put into the tank two years ago.

I had originally put in the black gravel to cover up the lighter colored gravel, but now after pulling out a good amount of vals with established root systems, the white gravel is starting to show again and I am thinking about adding some more black gravel to cover it up. I am concerned that if I do so, the calcium in the new gravel may cause a pH boost detrimental to the fish. Am I being overly paranoid, or is that a real possibility?


Thanks to those who have read this far.

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Last edited by Axelrodi202; 08-14-2012 at 03:27 AM. Reason: Added more specifics
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post #2 of 4 (permalink) Old 08-14-2012, 02:41 PM
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If you do lots of massive water changes then the tank will be more like the tap water, no matter what the substrate is doing.

If you do smaller, less frequent water changes then the gravel has more time to affect the water.

If you are seeing essentially the same results, tap and tank, then I do not think the gravel is having much of an affect on the water.

There is not one standard sort of pea gravel.
'Pea' is a word that describes size and shape, not the chemical properties of the gravel.
'Pea Gravel' is whatever rock is locally the cheapest that is roughly 1/4" diameter and more or less rounded.

Gravel or sand that affects the water parameters (mineral levels and pH) is most often rock with some sort of limestone origins, no matter what size and shape the rock it. It can even be the colored rock in pet stores. Once they put that colored coating on it that seals up the chemical properties until the coating wears off.

Burying active rock by covering it with more rock does not really solve the problem. There is enough water movement through most gravels (certainly through pea sized gravel) that the rock at the bottom is still affecting the water.

Here is what I would do:

1) Put a handful of the suspicious rock in a jar with tap water.
2) Test the water in the jar every few days for a week.
3) Run the test out as long as you want, testing weekly.

Test for GH, KH, pH and TDS.

pH is not a stand alone value. It is controlled by whatever minerals and salts are in the water. If the rock is adding certain minerals to the water then you will likely see those 4 tests rising.

Post the results here, and I can go into more details. There are other things the tank may be doing that offset the changes in pH. That would be important to understand.
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post #3 of 4 (permalink) Old 08-14-2012, 06:53 PM Thread Starter
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I do less frequent smaller water changes so I imagine the gravel is not having too much of an effect. It occurred to me to look at the bag the black gravel came in, and it says it will not affect water chemistry, so I'm assuming it's inert. The white gravel was added in 2003, so I no longer have the bag to check if it's inert. I was thinking of adding more black gravel for aesthetic reasons, not to attempt to cover up the possible effects of the rest of the gravel.

I am thinking of just replacing the gravel with black sand, so I don't have to deal with the white gravel re-appearing anymore. Any recommendations for any cheap inert sand?

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post #4 of 4 (permalink) Old 08-14-2012, 10:13 PM
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If you are looking for black, there are several possibilities, each product is slightly different.

Eco Complete is a reasonable substrate for planted tanks. It can hold fertilizers and keep them available for plants. It is not uniform sizes, but is black. It is usually a bit coarser than sand. The packages I got had a couple of chunks about 1/4" to 1/2", but mostly finer. Not very fine, though. Inert in terms of GH/KH/pH. There used to be more than one product available, and one of them was not inert for GH/KH/pH. Read labels very carefully.

Tahitian Moon Sand is a very fine sand, inert both in terms of fertilizer and GH/KH/pH.

Blasting sand, such as Black Diamond is often used as aquarium substrate. I have not used it. Look in masonry yards, and I think it is available in some Home Depot or Lowes types of stores. Inert both in terms of fertilizer and GH/KH/pH.
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