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post #1 of 25 (permalink) Old 08-14-2018, 02:56 PM Thread Starter
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New to TDS

I’m using a TDS meter for first time. Tested my tap water which was 275. Tank water after 40% water change was 325. Use PPS pro ferts as per the instructions. No wood. Fluorite substrate. Use daily API CO2 booster (ran out Of pressurized CO2 but will buy some soon), feed once a day. 12 gallon tank. Fully planted with about 1/4 of substrate carpeted. 3 dwarf Gouramis, 5 neon tetras, 5 Ottos, 5 Amano shrimp, 9 Nirite and bunch of hitchhiker snails. Nitrites and ammonia pretty much always zero. Nitrates around 30 after weekly 40% water change.
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Any comments on my TDS would be appreciated. What would be considered too high for my situation. I am hoping to use the meter to gauge when to do water change and such.

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post #2 of 25 (permalink) Old 08-14-2018, 03:05 PM
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weekly 40% water change.
Why change?

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post #3 of 25 (permalink) Old 08-14-2018, 03:14 PM
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Almost every substance added to the water will increase TDS: water conditioner, fish foods, plant fertilizers, medications, water adjustment products, etc. Often, if your GH is high, this will be the major component of a TDS reading.

A TDS range of 100 - 400 is acceptable, but targeting the lower end of the range is best. Be careful about TDS changes greater than a maximum of 50 ppm or 10%, whichever is greater. The osmotic pressure change can cause TDS shock in fish (what we used to - incorrectly - think of as pH shock). Allow a few days between changes of these magnitudes.
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post #4 of 25 (permalink) Old 08-14-2018, 03:21 PM
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That's a pretty heavy bioload for a 12 gallon tank. TDS readings only help when you know the exact composition of your water. A water quality report might offer some insight. You'd be better off using nitrate readings to determine water changes with your particular tank.
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post #5 of 25 (permalink) Old 08-14-2018, 03:41 PM
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Tested my tap water which was 275. Ö Any comments on my TDS would be appreciated. What would be considered too high for my situation.
Canít say because you didnít include what kind of TDS value, ĶS or ppm NaCl? There is more than one TDS system.
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I am hoping to use the meter to gauge when to do water change and such.
Greater TDS difference between tap and aquarium greater the need for water changes.
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post #6 of 25 (permalink) Old 08-15-2018, 06:54 PM Thread Starter
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my meter measures in ppm

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post #7 of 25 (permalink) Old 08-15-2018, 07:11 PM
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Tap TDS 275 ppm NaCl (564 ĶS) is very high. It is an indication of high GH and KH, or NaCl water softener.


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post #8 of 25 (permalink) Old 08-15-2018, 09:57 PM
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What TDS meter measures is electrical conductivity in uS/m, but for easy understanding, it is converted to equivalent ppm of Na or Ca using factors of 0.5 to 0.65 respectively, or some other factors based on assumption of the ions present. Your instruction may say what factor is used, but more often not. So comparing one tds value to another is not one to one, as it depends on the ions present. TDS is proxy of many things, such as salinity, hardness, level of pollution, or how long you havenít done WC.
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post #9 of 25 (permalink) Old 08-15-2018, 09:59 PM
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Dechlorinater will raise water too. TDS is basically a measurement of anything and everything in the water all in 1 reading. Completely useless without knowing what is in it.
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post #10 of 25 (permalink) Old 08-16-2018, 09:54 AM
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Tap TDS 275 ppm NaCl (564 ĶS) is very high. It is an indication of high GH and KH, or NaCl water softener.

Depends where you live. My tap TDS is 400 so I'd consider 275 hard but nothing to panic over



If your water changes keep on top of things you'd expect your TDS to be about the TDS of your tap plus 2 x the amount your ferts raise the TDS between changes. Measure your TDS before and after you add ferts (give it time to mix after). That's how much the ferts contribute.


I wouldn't worry too much about the actual number though - TDS measures all the 'stuff' but doesn't tell you what it is. What it does tell you is if you are keeping things stable. So measure over time, and if you see it gradually creep up you know you need to change a bit more water. Roughly, you want to reset your TDS at each water change so over time it stays stable. The stable number will be unique to you and will generally be a bit higher than your tap.
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post #11 of 25 (permalink) Old 08-16-2018, 11:55 AM
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Dechlorinater will raise water too. TDS is basically a measurement of anything and everything in the water all in 1 reading. Completely useless without knowing what is in it.
I think this is a good summary of TDS in so far it concerns aquarium keeping. I would add some things would not even register on a TDS meter. And as mentioned a TDS pen does not even measure TDS but tries to give equiv. with an unknown(to us) curve.

Use it to check if the RO unit works well, you got your remineralizer dosing right in pure RODI water and if the cooling water needs changing.

Different things can give the same TDS reading. Even for the things that the TDS can detect, the ratios between them can change in the aquarium while the TDS 'remains stable'.

Some people have argued a long time ago that you should do water changes based on the change in TDS. I raise an eyebrow and smile. I won't go into the arguments again, but take into consideration what was written above and in others' post, and decide if it is still good for your application.
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post #12 of 25 (permalink) Old 08-17-2018, 01:50 PM
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For my new build I am using conductivity or ec, a reliable method of measuring tds as long as you know the conversion factor for your meter (the Hanna ďdistĒ series uses a .5 conversion, so a measurement of 200 microsiemens on the meter represents a tds of 100 ppm), as the guiding metric for when I need to dose ferts, perform water changes, etc..

Iíve found ec/tds to be the most reliable and simple way to determine when adjustments to the water are necessary, and would definitely recommend it to anyone looking to fine tune their dosing/water change routine without having to test a million different parameters. It works whether you are using tap water or ro/di (although I think itís an even better indicator when using ro/di because you can control the exact make up of the tds in your tank).

With tap water (and rodi for that matter) you need to establish two baseline tds readings in order to use it as a determinitive metric- source water and baseline tank water. Letís say your water comes out the tap with a tds of 150ppm (or an ec of 300 microsiemens), and the water in your tank before ever dosing ferts or immediately after a 50% wc has a tds of 250ppm due to fish waste, nutrients released by substrate/driftwood/decaying plant matter.

The 250ppm number is the baseline in this example. If youíre using a dosing method like pps or pps pro- you would add ferts at the suggested rates until you observe a 100ppm increase in your baseline tds (350ppm in this example). Once your tds has increased by 100ppm, it is now time to do a water change to reset the tank back to its baseline of 250 (or as close as you can get).

This is where using tap water can get tricky- if you are replacing the 350ppm water with tap water that has a tds of 150ppm, you will need to change far more water to get back to your baseline than you would if you were using ultra low tds rodi water. My rodi unit puts out water with a tds of 1-2ppm which is exceptionally low for a home purification system. I wonít get in to the math, but one can clearly see that using 2ppm water for a change will be much more efficient at getting you back to your baseline than if you use water thatís 150ppm. You also have the benefit of knowing exactly what elements are responsible for a given tds reading when starting from 0 (or close to it) because you are adding them in. With tap water, the tds could be the result of any one or a combination of a number of elements that we cannot control for (in my town we have pretty high NACL and iron content in our tap, so those three elements are the main sources of tds but there are certainly others like calcium, magnesium, silica, etc. that also contribute. I strongly suggest going on your towns website and accessing your most recent water quality report to get an idea of whatís in your tap water).

Most of the elements that would raise tds in your tap water are beneficial nutrients for plants, but itís impossible to determine the concentrations of each without expernsive testing or very detailed and accurate town water reports. Again, this is why I prefer rodi water when using ec or tds as the determining factor. However, as long as you have a baseline to work from and your tap tds isnít higher than your target baseline tank tds, tap water or a mix of tap and rodi can work.

One last note on baseline tds- Iíve seen a lot of people both here and on other sites claim that tds values in and of themselves are worthless measurements- this may be true in a tank with no fish, but if you do keep fish in your fish tank lol the claim that tds is a worthless measurement is completely incorrect and I will gladly argue that point with anyone who wishes to do so.

Most of the fish that we commonly stock in our planted tanks (most tetras, rasboras, gouramis, non-rift lake cichlids, etc.) have evolved to live in low tds conditions and rely on the relatively pure water in which they live to remove contaminants from their bodies. A classic softwater tetra like a neon or cardinal will producd as much as 3.5 times their body weight in urine every day. They take in the ultra low tds water from their surroundings and use it to flush nitrates and other nutrients from their bodies. This works because they are adapted to the relative osmotic pressure of the low tds eater in which they live. If you place these fish in conditions where the tds is approaching the levels inside their bodies, their internal organs must work much harder to purge the nutrients from their bodies which places undue strain on their kidneys and liver, which in turn stresses the fish and weakens their immune system, shortening their lifespan and making them far more succeptible to disease.

Some Amazon biotopes have natural tds levels as low as 10-20ppm! Aquarists looking to succefully keep and or breed fish from such regions almost always rely on a rodi system for their water. Even then, levels this low are not really attainable in a planted tank setting, and would be problematic for the plants. You also have to make sure you provide enough mineral content to allow the fish to perform their metabolic functions.

Because I keep tetras from very low tds environments, I try to keep my baseline tds at around 120-150ppm and will change the water once it hits 200ppm. This is just the number Ive settled on based on what works for my fish and plants but everyone has to come up with a number that works for their set up. Observation of plant and fish health is the best way to make that determination.

There are plenty of people who keep tetras like rummy nose, cardinals, neons, etc. with tds thatís double mine, but as previously suggested, I would consider 500ppm to be the absolute cap on what constitutes a healthy low tds environment for Amazonian species and personally would not want to exceed 300ppm.

Many issues with fish that get attributed to ph swings or hardness are actually caused by osmotic shock, which can occur when fish are subjected to a large swing in osmotic pressure, measured by tds/ec. So contrary to a lot of the info thatís out there I believe tds/ec May be the single most important water parameter we can measure. If you are working with rodi water or known quantities of nutrients in your tap water, no other measurement will be as instructive for dosing and water changes as tds/ec. Period full stop.
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post #13 of 25 (permalink) Old 08-17-2018, 04:09 PM
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AdamRT ... Excellent post!

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This is where using tap water can get tricky- if you are replacing the 350ppm water with tap water that has a tds of 150ppm, you will need to change far more water to get back to your baseline than you would if you were using ultra low tds rodi water. My rodi unit puts out water with a tds of 1-2ppm which is exceptionally low for a home purification system. I wonít get in to the math, but one can clearly see that using 2ppm water for a change will be much more efficient at getting you back to your baseline than if you use water thatís 150ppm.
Example of cleaning 400L / 100gall aquarium from 300 ppm NaCl / 600 ĶS to 170 ppm NaCl / 340 ĶS with tap versus RO.

With 330 ĶS tap
30% WC, 600 -> 510 (- 90)
30% WC, 510 -> 450 (- 60)
30% WC, 450 -> 410 (- 40)
30% WC, 410 -> 383 (- 27)
30% WC, 383 -> 365 (- 18)
30% WC, 365 -> 353 (- 12)
30% WC, 353 -> 345 (- 8)
30% WC, 345 -> 340 (- 5)
Total amount of used water ≈ 1000 L

With 10 ĶS RO
30% WC, 600 -> 403 (- 197)
16% WC, 403 -> 340 (- 63)
Amount of used RO clean water ≈ 200 L
Amount of used RO waste water ≈ 800 L at 1 : 4 drain ratio
Total amount of used water ≈ 1000 L

It takes 8 water changes with tap water versus 1.5 with RO water while the total raw water usage remains the same.
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post #14 of 25 (permalink) Old 08-17-2018, 04:55 PM
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Very helpful
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Originally Posted by AdamRT View Post
For my new build I am using conductivity or ec, a reliable method of measuring tds as long as you know the conversion factor for your meter (the Hanna ďdistĒ series uses a .5 conversion, so a measurement of 200 microsiemens on the meter represents a tds of 100 ppm), as the guiding metric for when I need to dose ferts, perform water changes, etc..

Iíve found ec/tds to be the most reliable and simple way to determine when adjustments to the water are necessary, and would definitely recommend it to anyone looking to fine tune their dosing/water change routine without having to test a million different parameters. It works whether you are using tap water or ro/di (although I think itís an even better indicator when using ro/di because you can control the exact make up of the tds in your tank).

With tap water (and rodi for that matter) you need to establish two baseline tds readings in order to use it as a determinitive metric- source water and baseline tank water. Letís say your water comes out the tap with a tds of 150ppm (or an ec of 300 microsiemens), and the water in your tank before ever dosing ferts or immediately after a 50% wc has a tds of 250ppm due to fish waste, nutrients released by substrate/driftwood/decaying plant matter.

The 250ppm number is the baseline in this example. If youíre using a dosing method like pps or pps pro- you would add ferts at the suggested rates until you observe a 100ppm increase in your baseline tds (350ppm in this example). Once your tds has increased by 100ppm, it is now time to do a water change to reset the tank back to its baseline of 250 (or as close as you can get).

This is where using tap water can get tricky- if you are replacing the 350ppm water with tap water that has a tds of 150ppm, you will need to change far more water to get back to your baseline than you would if you were using ultra low tds rodi water. My rodi unit puts out water with a tds of 1-2ppm which is exceptionally low for a home purification system. I wonít get in to the math, but one can clearly see that using 2ppm water for a change will be much more efficient at getting you back to your baseline than if you use water thatís 150ppm. You also have the benefit of knowing exactly what elements are responsible for a given tds reading when starting from 0 (or close to it) because you are adding them in. With tap water, the tds could be the result of any one or a combination of a number of elements that we cannot control for (in my town we have pretty high NACL and iron content in our tap, so those three elements are the main sources of tds but there are certainly others like calcium, magnesium, silica, etc. that also contribute. I strongly suggest going on your towns website and accessing your most recent water quality report to get an idea of whatís in your tap water).

Most of the elements that would raise tds in your tap water are beneficial nutrients for plants, but itís impossible to determine the concentrations of each without expernsive testing or very detailed and accurate town water reports. Again, this is why I prefer rodi water when using ec or tds as the determining factor. However, as long as you have a baseline to work from and your tap tds isnít higher than your target baseline tank tds, tap water or a mix of tap and rodi can work.

One last note on baseline tds- Iíve seen a lot of people both here and on other sites claim that tds values in and of themselves are worthless measurements- this may be true in a tank with no fish, but if you do keep fish in your fish tank lol the claim that tds is a worthless measurement is completely incorrect and I will gladly argue that point with anyone who wishes to do so.

Most of the fish that we commonly stock in our planted tanks (most tetras, rasboras, gouramis, non-rift lake cichlids, etc.) have evolved to live in low tds conditions and rely on the relatively pure water in which they live to remove contaminants from their bodies. A classic softwater tetra like a neon or cardinal will producd as much as 3.5 times their body weight in urine every day. They take in the ultra low tds water from their surroundings and use it to flush nitrates and other nutrients from their bodies. This works because they are adapted to the relative osmotic pressure of the low tds eater in which they live. If you place these fish in conditions where the tds is approaching the levels inside their bodies, their internal organs must work much harder to purge the nutrients from their bodies which places undue strain on their kidneys and liver, which in turn stresses the fish and weakens their immune system, shortening their lifespan and making them far more succeptible to disease.

Some Amazon biotopes have natural tds levels as low as 10-20ppm! Aquarists looking to succefully keep and or breed fish from such regions almost always rely on a rodi system for their water. Even then, levels this low are not really attainable in a planted tank setting, and would be problematic for the plants. You also have to make sure you provide enough mineral content to allow the fish to perform their metabolic functions.

Because I keep tetras from very low tds environments, I try to keep my baseline tds at around 120-150ppm and will change the water once it hits 200ppm. This is just the number Ive settled on based on what works for my fish and plants but everyone has to come up with a number that works for their set up. Observation of plant and fish health is the best way to make that determination.

There are plenty of people who keep tetras like rummy nose, cardinals, neons, etc. with tds thatís double mine, but as previously suggested, I would consider 500ppm to be the absolute cap on what constitutes a healthy low tds environment for Amazonian species and personally would not want to exceed 300ppm.

Many issues with fish that get attributed to ph swings or hardness are actually caused by osmotic shock, which can occur when fish are subjected to a large swing in osmotic pressure, measured by tds/ec. So contrary to a lot of the info thatís out there I believe tds/ec May be the single most important water parameter we can measure. If you are working with rodi water or known quantities of nutrients in your tap water, no other measurement will be as instructive for dosing and water changes as tds/ec. Period full stop.
Very instructive- thank you. Makes me want to learn exactly what my EC monitor is really telling me on my Fluvel G6 filter. I do look at the changes it gives me before and after a water change, to see the difference of that number, but hadn't really taken the time to understand the implications of what it meant. Right now the EC meter says 230, its been 2 days ago that I did a 75% ( discus tank) water change. I will do another 1 tomorrow or the day after- Ill look to see what it is before and directly after doing so and then after dosing fertilizers. Typically the TDS runs about 115-120 in this tank. It sounds similar to the .5 conversion that you use.

However, lately ( the last 2 weeks) Ive been adding Equilibrium with water changes because was advised I had a magnesium deficiency in my plants. My KH is 3/GH 5.


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post #15 of 25 (permalink) Old 08-17-2018, 05:18 PM
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Edward can you please explain how one 30% water change and one 16% water change uses the same amount of water eight 30% water changes? Iím not sure what Iím missing but assuming an aquarium is 100 gallons, each 30% water change is 30 gallons of water. So eight 30 gallon water changes would require 240 gallons of water whereas one 30% change would be 30 gallons and the 16% water change would be 16 gallons for a total of 46 gallons of water changed:

240 gal > 46 gallons required to hit the target tds.

So it would appear to me that you can reach your target tds using about 1/5 of the total water when using rodi as opposed to tap.

Haha Idk what Iím missing, but Iím sure Iím going to feel stupid once you explain it.

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