TDS - plan or am I overthinking things?

[Ann D]

I have a 20 gallon long planted tank set up. Friday, I got a small shipment of rilis in (10). I did my first water change (2.5 gallons) last night and dripped the water in. However I noticed that my TDS rose after adding in the new water.

TDS of the tank was 283 before the WC; TDS of the water bucket was 220. I was assuming that if I replaced 2.5 gallons of water with water with a lower TDS the overall amount would be lower, not higher. I have to remineralize my well water (well water/tap is ph 6.0, ammonia/ITES/ATES 0, Cu 0, TDS 10, gh/kh 0-1). Last night, in order to get my well water close to tank parameters, I dosed with salty shrimp gh/kh until gh was 7-8 (tank is 8). Then I dosed salty shrimp kh until ph read 7.6 (like tank). Total kh was about 5 drops.

This brought the bucket up to about 200, then a couple of drops of Amquel+ and it was around 220. After the water change the tank read 304. My target TDS is around 260-280. Is there a formula where I can plug in variables to get a better estimate of "if new water is x, tank will show y"?

 

[wesleydnunder]

I have a 20 gallon long planted tank set up. Friday, I got a small shipment of rilis in (10). I did my first water change (2.5 gallons) last night and dripped the water in. However I noticed that my TDS rose after adding in the new water.

TDS of the tank was 283 before the WC; TDS of the water bucket was 220. I was assuming that if I replaced 2.5 gallons of water with water with a lower TDS the overall amount would be lower, not higher. I have to remineralize my well water (well water/tap is ph 6.0, ammonia/ITES/ATES 0, Cu 0, TDS 10, gh/kh 0-1). Last night, in order to get my well water close to tank parameters, I dosed with salty shrimp gh/kh until gh was 7-8 (tank is 8). Then I dosed salty shrimp kh until ph read 7.6 (like tank). Total kh was about 5 drops.

This brought the bucket up to about 200, then a couple of drops of Amquel+ and it was around 220. After the water change the tank read 304. My target TDS is around 260-280. Is there a formula where I can plug in variables to get a better estimate of "if new water is x, tank will show y"?

There is...it's a straightforward linear algebra formula. Your issue, I think, is in the accuracy of the test results from your GH, KH titration tests. For better accuracy, get a TDS meter and some calibration solutions. This will give you much more accurate tests and, therefore, much more accurate and repeatable results in your water mixing.

Mark

 

[Ann D]

I do have a TDS meter that I use (where I got my numbers). I do not have calibration solution, though.

 

[wesleydnunder]

I do have a TDS meter that I use (where I got my numbers). I do not have calibration solution, though.

Ah... when I saw this in the first post. " Total kh was about 5 drops..." I thought your were using a titration kit.

Mark

 

[Ann D]

No problem; I do have the test kits and use both (kit and meter)