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#### heel4you

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Hi everyone,

I have a question about how to figure out what Percentage of water change to do using PPS-PRO and my TDS meter.

Also, what is the PPM increase that tells me it is time for a water change?

I am including my TDS parameters to figure it out.

I don't use the Kno3 in my macros. My tank test Nitrate at 10-20 ppm always.

I have a light fish load in the 29 gallon:
6 Serpea tetras and one other small fish.
Heavily planted.

Tap: 95

Tank right now: 185

This is the TDS meter I have:

Amazon.com: HM Digital TDS-EZ Water Quality TDS Tester, 0-9990 ppm Measurement Range , 1 ppm Resolution, +/- 3% Readout Accuracy: Home Improvement Amazon.com: HM Digital TDS-EZ Water Quality TDS Tester, 0-9990 ppm Measurement Range , 1 ppm Resolution, +/- 3% Readout Accuracy: Home Improvement

I just need to know how to calculate what % of water change to do and when it should be done.

Thank you for any and all help

#### Edward

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I have a question about how to figure out what Percentage of water change to do using PPS-PRO and my TDS meter.
To find how large water portion (%) to change is dependent on three values.

Tap 95
Aquarium 185
Aquarium limit 130 (tap + 35 from fertilizer)

You will need to change 1 x 61% or 2 x 38% to get 130.

Also, what is the PPM increase that tells me it is time for a water change?
We are trying to find the answer here http://www.plantedtank.net/forums/11-fertilizers-water-parameters/1013169-tds-meter-4.html . Right now every meter gives different readings. So for now I would go with Bobbybills value of 35 ppm.

#### heel4you

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Edward,

So, to make sure I am clear.

Do these water changes to get to 130ppm.

Then, after it is set to 130ppm, I do my regular daily dosing until the ppm goes up 35ppm, then it's time for my regular water change.

Am I correct in this?

I have subscribed to the topic above, so I will be following to see if anything changes.

Thank you again for your time and expertise

#### Edward

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Yes, you need to change 1 x 61% or 2 x 38% to clean it up to the 130 limit. You can do more if you like, it doesn’t have to be exact as long as you don’t let it go over the 130 limit.

Your best bet is to maintain the aquarium TDS between [tap ] and [ tap + max fertilizer ] with water changes. It is between 95 and 130 for your setup. The easiest is to wait for the 130 and then change water as usual.

I would check the subscription again because once you post in a thread it activates the subscription. You may have deactivated it.

#### heel4you

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Thanks Edward.
I will check.
Thanks again for all your help!

#### Edward

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You are very welcome.
One more thing you can improve.
You mentioned you don’t add KNO3 in the macro solution. Without KNO3 addition, K is too low for the proper balance and need to be compensated by higher K2SO4 addition.

Here is the recipe in “What if my NO3 is too high with PPS-Pro dosing?” section.

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