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water change time


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I have been using SS GH+ on my neo tanks for a few months.

I do not keep an accurate note of the water level to do RO topoffs, so I really haven't done any.
My params at today's water change:
TDS 178
pH 7.6
GH 12 (ran this test twice for confirm)
KH 3
and the previous water change (18 days ago)
TDS 170
pH 7.6
GH 9 (ran this test once)
KH 3
Should I go ahead and add my remineralized water at 120TDS/GH4, or some RO, or what? 
I've kind of forgotten where the numbers should be, TDS in particular.
What TDS should I aim for on the tank? Or do you aim for a specific GH?
I never really understood how people pick a target number; it seems to be based on experimentation?
I'm also a little surprised that the GH is up that much in 18 days. 
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Honestly my first thought is if you are using an API GH test kit, spend at LEAST 5-10 minutes beating it vigorously on hard surfaces and then re-test several (3+) times.  The GH test kit can crystallize from solution and result in lower test (solution) concentration, which leads to higher test results.


Something about the TDS and GH seems fishy to me........interested to see if this changes anything.  

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well,if you don't do top offs with pure water and just do water changes,the gh will go up.

mark where the water level should be if you have a rimless or lower level under the rim.


i wouldn't worry about TDS in the tank unless it's super low or high,but the number is around 175-225.

i only use my TDS pen when mixing.


remove a little water and slowly add ro.

do a little bit each day till the gh is between 7-9.i shoot for 8.

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I have heard that about the nitrate reagent, but not GH.

I will certainly retest; my reagent is less than a year old, and I do give a brief shake before use, generally. Now I will be more vigorous.


Another data point: GH was 8 on Oct.12th, and that was confirmed by a second test.



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