What is the Proper TDS for an Aquarium?

How to Utilize a TDS Meter

Written by the Team at Atlantis Aquatics

TDS Basics

A TDS meter can measure all of the organic and inorganic material in molecular form in your water. This includes GH, KH, nitrate, nitrite, etc. Since they are in molecular form, TDS, or Total Dissolved Solids, can more simply be explained as the substances that can not be picked up by filters. Aquarium filters can only catch what comprises TSS (Toal Suspended Solids), which are material things such as plant matter or fish waste.

High concentrations of TDS can reduce water clarity and decrease photosynthesis in aquatic plants. It can also combine with toxic compounds and heavy metals leading to an increase in water temperature. You can use a TDS meter to keep track of how your TDS fluctuates.

So what is the proper TDS level for an aquarium? Unfortunately, the answer is not everyone’s favorite…

It depends…

Finding the Proper TDS

First, it depends on your fish. Some fish are used to native streams of nearly zero TDS water. Others, such as African Cichlids, can live in waters of TDS between 300-400 ppm. It also depends on various substances you may add to your fish tank. Nearly anything that you add to your tank will result in an increase in TDS (water conditioner, plant fertilizer, uneaten food).

TDS = GH + KH + Nitrate + Nitrite + Chlorine + Other Molecular Compounds

The desired level of nitrites and nitrates alike is zero for both fresh and saltwater aquariums. Although a nitrate level of less than 40 ppm is acceptable.

Chlorine is desired to be 0 ppm.

GH (general hardness) is the combination of calcium and magnesium ions found in water. Desired GH will depend on the fish you keep in your aquarium.

As you can see in the chart below, we know KH is typically between 120 and 180 ppm for freshwater and 180-300 ppm for saltwater.

So with all this info in mind, here is an example below this chart on how you can determine the desired Total Dissolved Solids level for your tank.

Computing Desired TDS for Neon Tetra Fish

TDS = GH + KH+ Nitrate + Nitrite + Chlorine + Other Molecular Compounds

  • Neon tetras desire soft water so GH = 60-75 ppm*
  • Neon tetras desire KH of 70 – 120 ppm*
  • Nitrate, Nitrite, Chlorine desired as 0

TDS = (60-75 ppm) + (70-120 ppm)+ 0 + 0 + 0 + Other Molecular CompoundsTDS should be between 130 and 195 ppm + what comes from compounds such as fish waste, plant fertilizers, algae treatment chemicals, etc.

*= Researched from various online articles and forums referenced at the end of the article

Using a TDS Meter

To find a base level of the Total Dissolved Solids coming from “Other Molecular Compounds”, use a TDS meter to measure the TDS of your tap water. This will give you insight as to what substances may be in your tap water. If TDS is over 300 ppm, not only will you want to consider drinking different water, but you may want to reduce the TDS before adding it to your tank. Mix 0 TDS water with tap water to get it to a range of 150-200 ppm before adding it to your aquarium.

Then, continuously monitor the TDS meter as your aquarium runs and as you add any kind of substance to your water. Once you have determined the average TDS of your aquarium from observing for a few days, use a test strip to make sure all of the individual compounds are at their desired levels (nitrate, nitrite, gH, kH, chlorine). If all of these levels are correct, the average TDS you’ve observed is your aquarium’s ideal TDS level. From there, you can keep an eye on your TDS meter and not waste test strips until you see a significant increase in TDS (approx. 10-15%). A spike in aquarium TDS would indicate that one of your tank’s levels is too high. From there, you can use a test strip to diagnose which specific level it is.

High TDS Levels

When TDS levels are too high, your fish are at an even greater risk of danger than your aquarium plants. Fish are largely comprised of water, and when they are in water with high TDS, the high TDS aquarium water wants to equalize with the lower TDS water inside the fish. The aquarium water attempts to pass through the fish until the levels equalize. This affects blood pH, digestion, and its immune system, greatly increasing the risk for disease.

One of the most efficient ways to keep an eye on your TDS is with a meter like this one! It’s cheap, accurate, and gives you instant results.

Plus, it runs off batteries so you don’t need yet another cord in the back of your tank! 

So what’s the best deal on a TDS Meter out there?

tds meter aquarium

Let me know what questions you may have and thanks so much for reading on monitoring Total Dissolved Solids in an aquarium!

Derek, Co- Founder of Atlantis Aquatics

IG: atlantis.aquatics

FB: Atlantis Aquatics


  1. Nico Fish-A-Day Farms

    Hi we are intersted in some of your producs so if yo can contac me @ 0722298853 please

  2. iamjackusa.wordpress.com

    Somebody essentially lend a hand to make critically
    articles I would state. That is the first time I frequented your web page and so far?
    I surprised with the analysis you made to make this particular post extraordinary.
    Magnificent task!

    • Atlantis Aquatics

      Thanks, Jack! I had the idea for it and then went out to gather some additional TDS info to be as accurate as I could with it.

      – Derek, Co-Founder of Atlantis Aquatics

  3. Sandeep

    Hi I am from Mumbai, India and have 8 goldfish in 2ft tank and shopkeeper gave me chlorine remover,anti-fungal solutions and some sea salt to pour in water 1/2 hr before putting fish inside to maintain good quality water for them, now I have checked TDS by my TDS meter and found it goes to 700-800ppm which have surprised me if this is ideal or not for them to survive, please provide your suggestion

    • Kevin White

      Sandeep, this is NOT advice . . . I could be way wrong and just lucky!

      I have goldfish as well and I live in an area where limestone is just below the surface. Our tap water is 700+ppm TDS and 8.3+ pH. I have healthy and happy goldfish. Hope this helps!


      • Radhakrishnan

        Hello Mr.Sandeep
        As you says the TDS IS 700 + it is dangerous for your fish.you immediately change the water with fresh one with no chlorine . You keep one separate bucket which has minimum 50% volume of your fish tank and store your regular tab water to leave it for minimum one day to reduce the chlorine in the water add de chlorine drops in it . Change the water in your fish tank by removing the fish poop and excessive fish food deposited in the bottom of the tank regularly by syphoning with narrow dia PVC pipe to suck the waste and poop effectively every day and add equal quantity of the old water you stored in the bucket .. Measure the TDS before cleaning the tank and after adding fresh water by which you stored in your bucket.
        Normally the fresh water in mumbai is about 50 to 70 TDS the filtered water would be between 40 to 50.( Aqua guard filtered eater)
        Now measure the Tank water TDS if it is above 200 TDS. You replace further offered water in it to maintain the TDS below 200TDS. and check the pH and maintain between 6.5 to 8.0 pH .For optimum pH in the tank .Don’t add much of sea salt it will I crease TDS which is not good for your Gold fish.
        You buy TDS & pH measuring kit from Amazon which is handy to maintain the fish tank TDS and pH level..
        You regularly search Google for getting tips to maintain your fish tanks..I learned a lot from the Google only and following to maintain my fish tank of your same size with 10 fish .
        Hope you can get better knowledge through Google..

    • Mark Britland

      Water changes!

    • Tristan

      Hi there.. i have read this article and im very impressed, I learned everything I needed to learn about tds..
      I was after some advice on my tetra tank.. i only have a tds reader at the moment that came with my zero-water filter i ordered for myself.
      I tested my “what I thought to be” prestine tank water. And the readings are between 600-700!!
      I’m going to do a tank overhall with all new lighting, decor, substraint, plants etc and was wondering your advice on how to get my water tds down and to keep it down in the future??

      I have got neons,rummynose’s, glowlights, king blue’s and Congo tetras.. plus a plec and a neon blue crayfish..

      Any advice would be great. Thanks in advance

      • Atlantis Aquatics

        Hey Tristan! Thanks so much for your kind words!

        Here’s where it could be coming from.
        1) Not frequent enough water changes (do 50% weekly)
        2) No bottom feeders to help clean up food that falls to the bottom. This is more necessary in a community tank like you have.
        3) Not enough live plants to help soak up excess nitrates

  4. Leonard

    You made some good points there. I checked on the internet for additional information about
    the issue and found most people will go along with your
    views on this site.

  5. joe h

    what is a good tds for discus. i use ro/di water and remineralize with discus minerals which i buy from germany. this method keeps my tds at 80-100. my ph -6.4 / gh-90ppms / kh-17ppms/water temp 85 degrees. this seems to work great for discus and plants.

    • Atlantis Aquatics

      The best TDS for Discus fish is typically between 200 – 300 ppm but your tap water’s base TDS may play into this a little bit. Lower than 200 – 300 is less problematic than higher but I would check every level individually to see why it may be playing out this way.

      • Abhishek Kumar

        What is best tds for Asian Arowana, after adding all the chemicals my tds value is 210 & pH is 7.4. my tao water tds remains somewhere between 70 to 90 + seachem prime + stability + seachem arowana buffer (phosphate based) , without buffer it stays at 120 , but using buffer to lower the pH, please suggest.

  6. Alec

    Are you sure you paid attention in biology classes? I doubt, when I see your TDS calculation + advise …

    • Atlantis Aquatics

      Do you have a specific thing you are questioning?

  7. Jimmy

    Great post. Taught me everything I wanted to know about TDS!

  8. Mike

    Having major diatoms issue. Have consistently cleaned plants outside the tank and ornamental rocks, driftwood, equipment. Repeatedly for weeks with many water changes. By day 3 / 4, they’re back! Do I have to completely remove the type of sand I have and start over? Help, very frustrated!

    Thanks in advance any advice you can give that I haven’t already tried!

    • Nicholas Pet

      Try lowering your lighting time, or add half the ferts

  9. Flavian

    How to increase TDS in my aquarium take

    • Atlantis Aquatics

      TDS will naturally increase over time or any time you add a chemical to it. Reducing TDS is what you need to worry about.

  10. Instructor Brittany

    Testing the water is a great way to check the quality of water that you receive and use for different purposes. Here are some reasons you need to measure TDS in water. Taste- High levels of TDS in water affects the taste of your drinking water. Your water may taste bitter, salty or sulfuric depending on the type of dissolved solids present in water.

  11. Amy

    I use ro water and remineralise with seachem equilibrium, alkaline and acid buffers, my water starts at 0 TDS and once remineralised is 325 TDS, you are saying that is too high?? My GH is 5, KH 3 and PH 7.

  12. Alex L.

    Unfortunately, your calculation of TDS in a freshwater tank does not take into account chloride, sulfate, sodium and potassium ions. All of them are not only present in tap water, drinking water and even in the remineralized water from a reverse osmosis system, but they are highly desirable and even necessary both for us humans and for tropical fish. In fact, the above ions add to your calculations ~ 200-300 ppm. A freshwater tank whose TDS is 360 or even 470 is quite okay as long as the levels of nitrates, nitrites and other problematic ions remain low enough.



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