Water people - Question about TDS and Nitrates - The Planted Tank Forum
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post #1 of 19 (permalink) Old 12-20-2015, 07:11 PM Thread Starter
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Water people - Question about TDS and Nitrates

More and more I have been seeing questions about the TDS on people's tanks as people are trying to dx problems. So - I decided to read up on TDS and buy a TDS meter. This morning I measured my water straight from the well, out of my RO filter, sink, and distilled.

TDS
Well - 648 (liquid rock I believe that is called)
RO - 41
Sink - 664
Distilled - 1

PH
Well - 7.6
RO - 7.0
Sink - 7.8
Distilled - 6.7

So - I then tested my tanks. This is where my question comes up.

Tanks Background

I have been experimenting with the different tank types and seeing how the plants and fish do in the different environments.

75 gallon planted tank: Running for 1+ year - ADA Amazonian substrate, heavily planted, drift wood, some rocks. LED lights (75% - 8 hours) 2 Eheim Canister Filters, water changes every other week with top offs during the week. Fertilizer once a week - Flourish. 10-12 Tiger Barbs, 10 Gold Barbs, 6 Corys, 5 Amano Shrimp

20 gallon planted tank: Running 3 years - Gravel, root tabs, medium planted, drift wood. T5 (10 hours) HOB filter, water changes every couple months with top offs. 8 Cherry Barbs and a clown pleco. Very heathy fish and 3 of the barbs were born in that tank.

10 gallon planted tank: Running 6 months - Dirted with black diamond blasting sand cap, medium planted, lots of floating water lettuce. T5 (10 hours) Internal filter, water changes every other week. 2 GBRs, 3 pygmy cories.

5 gallon planted tank: Running 9 months - Dirted with black diamond blasting sand cap, heavily planted, water lettuce. T5 (8 hours with siesta) No filter, quarterly water changes. 1 Betta


75 gallon: TDS 951, PH 7.6, Nitrates 10
20 gallon: TDS 105, PH 7.4, Nitrates 80
10 gallon: TDS 715, PH 7.2, Nitrates 5
5 gallon: TDS 765, PH 7.7, Nitrates 0


I cannot figure out what is going on with the 20 gallon. Why is the TDS so much lower than the rest of the tanks? I expected the Nitrates to be high due to less water changes but I also expected the TDS to be higher.

The 75 gallon makes sense, more heavily stocked, higher TDS and Nitrates make sense.

Off to do my water changes....
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post #2 of 19 (permalink) Old 12-21-2015, 06:19 AM
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Quote:
20 gallon: TDS 105
Unless you did a water change with RO water - cannot believe the test.

If you have a choice, you have a problem, till you elect your choice. No choice, no problem, only consequences, learn to live with them.
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post #3 of 19 (permalink) Old 12-21-2015, 08:47 AM
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might be TDS is 1050 but your meter does not show last digit
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post #4 of 19 (permalink) Old 12-21-2015, 09:29 AM Thread Starter
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Quote:
Originally Posted by essabee View Post
Unless you did a water change with RO water - cannot believe the test.

I didn't do an RO water change. However I did check it 4 times and always the same result.

Quote:
Originally Posted by dzega View Post
might be TDS is 1050 but your meter does not show last digit

This might be the case. I will have to check the meter. It would make sense and tie out to the water conditions.

I did ask my husband to get some water out of the creek behind our house (he had to break through the ice - nice guy ). I was curious to compare against our well. It measured 480.

I am thinking I need to switch the plans for my next tank. I am planning a South American River tank - maybe I need to change it to Lake Tanganyika.

Thanks for your replies.





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post #5 of 19 (permalink) Old 12-21-2015, 09:30 AM
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Less water changes should mean that the 20 gallon has a higher TDS. As you do top ups, the TDS builds. With a water change, TDS should stay the same or decrease given your tap water.

I agree that the result is in fact 1050 TDS.

I would bet my left nut on it.
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post #6 of 19 (permalink) Old 12-21-2015, 12:54 PM
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Simple test

Quote:
Originally Posted by dzega View Post
might be TDS is 1050 but your meter does not show last digit
To jlfkona: Take 1L of tank's water (measure TDS), then add 1L of distilled water to it, stir it up, and measure TDS again.
If your original TDS was really 105, you should be reading 50 TDS on your meter; if your original TDS was 1050, you should be reading 500. Simple test to verify your results.
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post #7 of 19 (permalink) Old 12-21-2015, 01:32 PM
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Originally Posted by Marcel G View Post
To jlfkona: Take 1L of tank's water (measure TDS), then add 1L of distilled water to it, stir it up, and measure TDS again.
If your original TDS was really 105, you should be reading 50 TDS on your meter; if your original TDS was 1050, you should be reading 500. Simple test to verify your results.
This is actually a very good suggestion. I am curious if the OP will try it out and share?
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post #8 of 19 (permalink) Old 12-22-2015, 12:02 AM
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Curious, what should TDS of RO expected to be, close to 0?
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post #9 of 19 (permalink) Old 12-22-2015, 04:57 AM
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The definition of purified water is a TDS count of less than 10 parts-per-million (PPM), and both distilled water and purified water have between zero and one PPM.
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post #10 of 19 (permalink) Old 12-22-2015, 05:09 AM
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My ro is 3 to 6 tds. Tap 215 tds.

Bump: Fitters and membrane about 14 months old. Going to order new filters soon.
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post #11 of 19 (permalink) Old 12-22-2015, 05:33 AM Thread Starter
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Quote:
Originally Posted by Marcel G View Post
To jlfkona: Take 1L of tank's water (measure TDS), then add 1L of distilled water to it, stir it up, and measure TDS again.
If your original TDS was really 105, you should be reading 50 TDS on your meter; if your original TDS was 1050, you should be reading 500. Simple test to verify your results.

Thanks - this is a good idea. I am away from home tonight so I will give this a try Tuesday or Wednesday.


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post #12 of 19 (permalink) Old 12-23-2015, 04:43 AM
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Quote:
Originally Posted by jlfkona View Post
Quote:
Originally Posted by Marcel G View Post
To jlfkona: Take 1L of tank's water (measure TDS), then add 1L of distilled water to it, stir it up, and measure TDS again.
If your original TDS was really 105, you should be reading 50 TDS on your meter; if your original TDS was 1050, you should be reading 500. Simple test to verify your results.

Thanks - this is a good idea. I am away from home tonight so I will give this a try Tuesday or Wednesday.


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Okay it's Tuesday what are the results?

My attention span is short, please hurry.
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post #13 of 19 (permalink) Old 12-24-2015, 01:38 PM Thread Starter
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Drum roll please.... Here are the results.

TDS straight from the tank: 102

TDS with 50/50 tank water and distilled water: 585

The meter only shows three numbers.

Thanks everyone for your help!


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post #14 of 19 (permalink) Old 12-24-2015, 01:47 PM
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Thankfully my left nut is safe.
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post #15 of 19 (permalink) Old 12-24-2015, 08:14 PM
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Cheap ebay meters have a "x10" symbol in the display to denote values greater then 999ppm.

Feel free to edit.
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