Terrible Advice Tuesdays: Clean Saltwater Tank = Low TDS?

Terrible Advice Tuesdays: If you want to find out how clean your tank water is, just stick a TDS meter in it!

The rest of the story: I nearly fell out of my chair when I read this one. A TDS meter will give you an “error” or “inf” reading if you stick it in a saltwater tank. The amount of dissolved solids in even clean saltwater is off the charts so relying on a TDS meter to give you an indication of water quality in your tank is a waste of time.

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Comments for this article (18)

  • Josh says:

    Very true, I took a sample to work just to see what the TDS would be. The meter goes up to 10k, when I pressed the button it flew past the 10k and still had gas!

  • satwinder sarmotta says:

    Hi Mark,

    that sounds very silly lol, correct me if im wrong but isn’t a TDS meter to be used with an RO\DI unit to test the TDS in the product water?

    just a side note my TDS is reading 0.04 is this acceptable?



  • Lyle says:

    Just more bad info from someone who doesn’t know anything about the hobby! Just like that young kid who was giving advice when I knew his tank was going to crash by his second update video! We need some advice cops instead of tang cops! LOL!

  • Michael Willey says:

    So very true. Even if you could use it. It wouldn’t differentiate between nitrates, ammonia, nitrites, heavy metals, etc. If it read the ammounts…

    Sarmotta, the lower the reading the better. Especially if you have hightds from the source before the filter. My source is around 900 on the stick. After the to unit it reads 45. My do unit should be here this week. Hopping that drops it to 0.

  • satwinder sarmotta says:

    hi Michael

    my source water is just under 300 and product is 0.004 so i guess thats a good thing?

    its been used for 6 months at approx 3 days a month, and have half a bag of DI membrane left so could just replace that soon.

    just making sure i have the best possible water for my fish family 🙂

  • JasPR says:

    TDS is extremely broad as it measures almost ‘everything’ in water. I’ve never tried it but in theory it could be very useful in a different application- namely, measuring ‘change’ in TDS. This means that it could potentially provide a base line reading and then a higher reading as water deteriorates with time. In other words, a TDS reading climbing could tell you how quickly your water deteriorates with time between water changes OR when it is time to DO a water change. In this regard it might be more dependable then the difficult to track ORP reading. JasPR

  • Greg says:

    Here’s a great idea! Just do regular water changes and you don’t have to worry about deteriorating water and

  • satwinder sarmotta says:

    Greg, the water being produced from the RO\DI unit is for water changes, not baths lol

  • Tony V says:

    All I have to say is LMFAO

  • Harlan Mondrow says:

    I am new to Terrible Tuesdays but it has been my observations, that many of these “terrible Ideas” you come across Mark, knock you out of your chair.
    Butt must be getting sore, no? 🙂

  • Glenn says:

    For the RO/DI questions, mine is always at 0.00, when it shows 0.01 I change the filters. Also I let it run for 5 mins before testing, sometimes when it has been not in use for a few days the first few mins will show 0.01 but drops to 0.00 after its flushed out with new water. If Mark came up with a classification beyond Reef Junkie I’d fall into it.

  • James says:

    My incoming TDS is 0.03 and out going is 0.00 I use a BRS 5 stage RO/DI until and change the first filter after every 1000 gallons of water made and change other filters when the output is anything other than zero. I make 100 gallons a week.

  • Rebecca says:

    Hi! Newbie Reef Enthusiast here. What does TDS stand for? I’ve not heard of this before. How are you supposed to use one? Thanks a heap!

  • Rocko says:

    TDS= Total Dissolved Solids

  • Pierre Bouic says:

    Millivolts meters IE. Redox measurements are & will always be the most accurate view of water quality provided the probe is wiped every second day with a soft cloth. It’s old school stuff but is state of the art for scientific people will all agree. There is no existing TDS meter that works is salt water. Jaspr you’ve not making sence. A TDS meter is for small unit testing of fresh water, in salt water it’s like dropping a thermometer in lava.

  • Actually you can measure the TDS of saltwater but you have to use a conductivity probe. I wrote an entire article about it here http://nautilusaquaticsohio.com/secrets-of-a-healthy-reef-aquarium-using-conductivity-tds-in-your-water-mixing-equation-and-food-for-thought-on-artificial-salt-mixes/ seriously dude you have not been doing saltwater tanks long enough to have a show, or a book or anything…LOL

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