Terrible Advice Tuesdays (T.A.Tues): Low pH In Your Saltwater Tank? Time Kiss Your Sand Bed Goodbye

Terrible Advice Tuesdays: Your pH is below 8.1. That means your sand bed is currently dissolving into solution. You need to raise your pH if you want to have any sand left in your tank

The rest of the story: I always laugh at this one. Ever wonder why calcium reactors (which dissolve aragonite, aka large particle sand, and coral skeletons) are maintained at a pH of 6.5-6.7? That’s because at that low of a pH the calcium/aragonite actually dissolves at a rate that’s worth noting!

If your pH is below 8.1, your sand bed isn’t going anywhere.

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Comments for this article (16)

  • steven says:

    My tank sit at about 8.27 in the day and about 7.76 at night do I have anything to worry about or is there any way to get those numbers to balance out its a nano tanks there isn’t a bunch of room for extras

  • Crawford says:

    Hey Steven

    PH can be affected by things like light, so if your light is on all day and then turns off for the night, you are going to have a small PH shift. It’s not that big of a deal because it happens gradually, not the instant the light switches off. Swings of any kind aren’t a big deal as long as they’re gradual. Often times, tank owners will freak out and try to fix an issue they spot in an instant, which then causes big problems.

  • Frankie says:

    Who gives that advice??? That’s just plan crazy…

  • steven says:

    Thanks Crawford I have been monitoring it I was pretty sure it wasn’t a big deal but just wanted to make sure

  • Geraud says:

    You have to remember that pH is a log10 representation of concentrations.

    Which means that between 7.5 and 6.5, the latter is 10 times more acidic than what you have. So you should be more than fine at 7.76.

  • That advise was given by someone who read something that was true, did not understand it so when he explained it to someone else he just came up with a load of rubbish, i suggest that you try and grasp every bit of info you are reading or viewing, because its a fine line between right and terribly wrong!!! I had to laugh though!!!! one more fore the Reef Joke Book!!! thank’s 🙂

  • Micah says:

    I would be interested to know what the alkalinity level of you tank is. Not the a .5 swing is a huge deal, but maintaining a higher alkalinity level may help limit the swing.

  • David says:


    .5 was about the shift I would get from my tank’s daytime high to its night time low.
    As others have posted not that big a deal, but for the sake of stability, I happen to run my top off at night and I dose alkalinity then, too. Not too much. Just enough to keep the shift to .25 – .30.

  • steven says:

    I use Kent two part and try to keep my calcium around 430 and my alk between 8 and 10 dkh it’s a 16 gallon tank I do 2.5 gallon water changes a week and dose two part as necessary through out the week. I’m thinking of Using kalk with my ato instead of two part.

  • Wade says:

    Hey Stephen

    If you run a light in your refugium at an oposite schedule from your daytime DT light, then your pH swings will be much lower. I have my refugium light coming on at 10:00PM and turning off at 10:00AM.

  • John says:

    Someone trying to sell something to someone that they do not need at LFS.

  • Matt says:

    Did the person or persons who suggested this one attend basic chemistry at school?

    Good grief!

  • James says:

    Hey mark, have you ever heard of or used the “kalk king” system? I have one and it’s awesome. You should check it out and do a review

  • Richard M says:

    I can’t help but laugh at this one, I have been in this hobby for over 30 years… before people had internet in their homes, and sometimes I feel like the old days had their advantages…the spread of misinformation is astounding. One of the oldest rules of reef tanks is DON’T CHASE PH. CO2 is the biggest culprit of low ph and is easily corrected. I have found over the many years and many tanks is that most newer tanks naturally have lower ph levels and as the chemistry in the tank matures the ph level also rises. 7.8 range is fine.

  • Mike M says:

    Richard M is correct. Especially in a small tank. I started with a 10 gal. tank years ago and my ph was up and down due to CO2. It has little effect on my 75 gal. tank. I live in a small 40′ ranch with 3 people. With the doors and windows shut most of the day, the ph drop drastic overnight with no light. Keep the windows open for a couple of days and see is right up there at 8.1. I work with gas detection equipment and have access to CO2 monitors. Overnight with 3 people in the house, the levels of CO2 averaged 2500 ppm in the morning. Very high indeed. To give you an idea of how high this is, the average levels that we breath outdoors are around 400 ppm. 2000 ppm can give someone headach symptoms after 2 hours of exposure.
    I don’t get headachs, I am just loosing my mind.

  • Cliff says:

    Read Richard M below….

    I agree with everything he states even though I am new to the hobby. My reef is 8 months old and my ph swings between 7.8 to 8.0. With all my other parameters perfect, the real culprit was excess CO2 in the house. I have a brand new energy star efficient home (air tight). In Houston the weather is just now cool enough to open the windows. Surprise my tank ph is lovey now. add some good house plants and micro algae to aid this problem when you cant open windows. To see if you have a similar problem take some if your aquarium water and let it sit outside with a powerhead. If your ph raises to much co2 in the house.

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