Sand And Ph Experiment

[Akasha72]

A little under a year ago I decided to do an experiment to see why there was such a large discrepancy between my tap water and my tank. I'd long since suspected that my sand substrate was the culprit as at the time I was running another tank which had gravel as substrate and the pH in that tank didn't fall far from the tap level at all.
 
So, I got myself 3 drinking glasses, washed both and filled them both with boiling water to sterilize them. I filled each with an equal amount of dechlorinated water
 

 
I tested the pH on all three - all were exact.
 
Next I took a handful of sand from my Rio240 and a handful of gravel from my Rekord 800. I washed both well
 

 
I added the sand to glass one, the gravel to glass 2 and left glass 3 with just the plain water
 

 
I left all three glass uncovered on a shelf and tested the water daily
 
Over the period of around a week I gradually watched the pH in glass 2 (with gravel) fall and then become stable. Glass 1 though continued to fall though
 

 

 

 

 
The test tubes are from left to right - left being glass 1 with sand, middle being glass 2 with gravel and right test tube being the plain glass.
 
After around a week I ended the experiment as I felt I'd proved my point. Had I of carried on I truely believe that the pH in glass 1 would have fallen further
 
 

this is what my sand is
 

 

[Gvilleguy]

Interesting post, Akasha. Based on the colors there I'm guessing that was pH 6.0, 6.4 and 7.0, left to right! I have been doing a similar experiment on an empty 6.6 gallon tank I have. I am trying to determine the proper level of crushed coral in the substrate to maintain a pH of 7.0. My tap water settles out to 6.0 in my tanks unless I buffer it with coral.

 

[Byron]

I'll jump straight to the issue, since I know the background.  I would suggest that the sand contained organic matter and bacteria in it, notwithstanding the washing; we know that washing in tap water is not going to remove or kill much of the bacteria, and it may have withheld some organic matter too.  There is also the organic matter present in tap water [this causes the bacterial blooms in new tanks].  You also dechlorinated the water which likely encouraged the bacteria even faster, though again the chlorine in the tap water may not be the "killer" we have formerly believed it to be.  The gravel seems to have had less.  This is why sand and gravel are such excellent substrate materials.  From the other thread, I also know that your KH is very low, 1-2 you wrote, so the higher organic/bacteria content in the sand allowed a greater drop in pH.
 
Sand and gravel are made by crushing rock.  When submerged, sand/gravel will slowly dissolve the mineral contained in the rock; if this mineral is calcareous, the mineral content of the water may increase, causing a rise in the GH, KH and pH.  If the rock is inert, there would be no effect on the GH/KH/pH.  I am not aware of any natural rock that will result in the lowering of these parameters, but organic matter added to or contained within the sand/gravel could lower the GH/KH/pH.  
 
The only way to lower pH is to add an acid to the water.  CO2 does this because it creates carbonic acid, which is why we have to out-gas the CO2 from tap water before testing pH.  Organic matter is the normal way this occurs in nature, as CO2 is produced in considerable quantity from the breakdown (decomposition) or organic matter.
 
Byron.

 

[Akasha72]

but surely as the Rekord 800 (containing the gravel) which had been a running established tank far longer than the Rio would have had far more organics in the substrate. If it were down to organics both substrates would have reacted in the same way

Hi Gvilleguy - yes my Rekord 800 which contained a gravel substrate, ran at a steady pH 7 (the tap being just a little higher at around 7.2 - 7.4) The Rio runs at pH 6. It's remained a stable pH 6 for nearly 2 years and it's fine for my amazonian stock. I have some coral in my filters but it doesn't really do much to help

 

[Byron]

but surely as the Rekord 800 (containing the gravel) which had been a running established tank far longer than the Rio would have had far more organics in the substrate. If it were down to organics both substrates would have reacted in the same way
 

 
No, Akasha, you can't make that inference.  Sand is more porous than gravel, hence it holds more bacteria and such.  We also don't know from what rock the sand and gravel were crushed, so the gravel might have a different component (something calcareous).  We also don't know the other factors that play into this.
 
Byron.

 

[Akasha72]

okay ...

 

[Byron]

I just noticed something else from the photos you added.  The water in all three glasses in the first photo is clear as one would expect.  Moving to the photos of the glasses with the substrates added, the water in the sand glass has a slightly hazy (cloudy) appearance, and the gravel water is less so, with the plain water clearer still.  This could be a trick of the light/photo, but if it is actually cloudy, that would of course mean more bacteria and organics are present in the sand, and a bit less in the gravel.
 
I perused the Unipac site for some data on the material from which their gravel is made, but no luck.  I can't see all the writing on the bag in the photo...does it by chance say the origin rock?
 
Byron.

 

[Akasha72]

no the glasses never went cloudy. This experiment was August last year and so the sun light was messing with the colours etc - you can see from the photo's how bright the sun was. My living room window faces south so gets the full glare of the sun. 
 
As for the bag ... I'm not sure where it is. I'll have a look for it in the shed tomorrow. I seem to remember looking at their site myself at the time and not being able to find out what this sand is made from

 

[PrincessKiara]

Why not try the experiment with clean, unused sand and gravel? That would dispel all doubts, I believe

 

[Paradise3]

I use Unipac sand myself and I don't have a drop in pH. Even though I also have redmoor wood in there and it's a planted tank the pH is the same as what the tap water is.

 

[TwoTankAmin]

According to the Unipac site their gravel is coated. This should mean it is pH neutral.  http/www.unipacpet.co.uk/aquatic/micro-gravel/
 
What brand/type is the sand?

 

[Akasha72]

it's my sand that's Unipac TTA - my gravel is just one that my lfs sell and I'm unaware of the brand. What I do know is it's never messed with the pH. It's falls to neutral (from 7.4) and stays there
 
 
I am a little bit tempted to remove the sand and replace for the gravel. The gravel is very small and soft enough for cories although we all know sand is best for cories and that is what's making me dither over removing it. 
My tank is due to be drained and all fish removed in 2 weeks time due to a new carpet being fitted in the room and if I am going to change it - this would be a good time. I just want the best for my cories and gravel isn't it - even if it's small and soft enough for them.
 
Perhaps we can have a discussion on it here?
 
 
Another things though .... when I set up a breeding tank for my Angels last year I used playsand from Argos. This also dropped the pH to 6 and no-one can say that was organics because it was newly set up and it fell to pH6 within a week. There was no bogwood in there to blame either. Perhaps my water just doesn't like sand!!

 

[Byron]

Another things though .... when I set up a breeding tank for my Angels last year I used playsand from Argos. This also dropped the pH to 6 and no-one can say that was organics because it was newly set up and it fell to pH6 within a week. There was no bogwood in there to blame either. Perhaps my water just doesn't like sand!!
 

 
Akasha, you know how dirty play sand is; it is impossible to get all the dirt out, and there is the source of your organics, plus the tap water which contains a lot of dissolved organics.  And your low KH (like mine) means the pH will naturally lower fairly quickly once things get going biologically.
 
Believe me, no true sand or gravel that is made from crushing natural rock and has nothing else added in its composition will lower water parameters.
 

I am a little bit tempted to remove the sand and replace for the gravel. The gravel is very small and soft enough for cories although we all know sand is best for cories and that is what's making me dither over removing it. 
My tank is due to be drained and all fish removed in 2 weeks time due to a new carpet being fitted in the room and if I am going to change it - this would be a good time. I just want the best for my cories and gravel isn't it - even if it's small and soft enough for them.
 
Perhaps we can have a discussion on it here?
 

 
Gravel is not good for corys.  Aside from the sharpness issue, it is important that they have sand to sift through their gills.  Once you have cories over sand and observe their natural behaviour in doing this, it makes sense why they should never be over gravel.  Don't sacrifice your fish's well being for something else.
 
And just what is the issue that makes you think the sand should go?
 
Byron. 

 

[TwoTankAmin]

Here is the thing, The term sand refers to grain size, not the mineral content. When one begins to research sands and pH you will be hard pressed to find those which lower pH. Most tend to either be neutral or to raise pH. So far the only type of sand I have seen that lowers pH is gypsum sand and it is not suitable for tank use- its primary use is in making plaster and drywall.
 
It is not easy getting information on Unipac from the company. they only want to deal with retailers not end users. However, I did find a page for colored sand which indicated it was also coated.
 
But lets go at this from a different direction. Why not try to find sand that is known to lower pH in water. If this is a common thing, Google should find it fast. I can tell you I cannot find any sand that lowers pH aside from gypsum which would not be suitable for tank use. It is what they make plaster from among other things.
 
For sand, or any other substrate to change the pH in a tank, it must be dissolving. If one puts a bag of coral sand into a filter, over time it vanishes as it dissolves. The same applies to rocks in a tank. Just ask any rift lake cichlid keeper. But these sands and rocks are used because they raise the pH.
 
I would go with what Byron is discussing or else I would look elsewhere for the cause of what you are seeing.

 

[Akasha72]

well the issue really is water changing is becoming hard work. The tank - tap discrepency makes me worry and it means I can't really change as much water at once as I'd like and now my Nitrates are creeping up too high ... if the tank was closer to my tap pH level then I'd be able to change larger quantities of water and get the Nitrate down further .... but then I've got another big problem with my tap water too and it's causing BIG troubles. I have a phosphate level out of my tap of 1.8ppm - according to my test kit that is already in the danger level. Everytime I water change I add more phosphate, my phosphate remover in my filters has to work hard to bring the level down. I'm fighting a losing battle with that and it's starting to stress me out. Now my fish are sick again and everytime it seems to connect to high phosphate readings ... this has been a battle I've been trying to win for over a year and I'm at my wits end with it. 
 
I know your right over the sand - it could be an incredibly cruel thing to do to my cories and the more I think about it, the more I think it's a really bad idea. Yes, it would solve one water issue but no amount of changing of substrates is going to cure the phosphate issue - have a look at my other thread "body flukes ... again" - this is what happens everytime my phosphate level gets too high for too long
 
 
Sorry guys ... really stress today and not a happy fish keeper