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My PH pen went swimming


Jul 24, 2019
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Well the nutrients I use are a decent shade of brown, I don't know how the gro tek is but when the fluid is in the test tube it looks considerably lighter, and even with a base tint in the nutrient, it's really obvious to see how it changes reliably with the indicator drops. You just have to check it out yourself. And once you use a pH meter to calibrate what the colour should look like at particular pH's then you're golden. I will emphasise again that if you needed to go outside the range of 5.5 to 6.5 these drops would not be as useful. That is because it's easy to see a Red/Green swing on either side of the neutral Yellow, but you don't get that opposite contrast swing further down.

But for me the main reason I use drops is that I just got tired of continually checking calibration, then finding my fluid went mouldy and have to mix up another, or buy another buffer, it's was just a total pita. And the reason for this is that I'm just not prepared to go and make a radical change based on me trusting the pH meter. But that's just me. It's not for everyone. I like simple. Simple is good. The less unnecessary work I need to do the more I get to enjoy looking at the plants.

I used a pH meter side by side with the drops for a year, then when the pH meter broke, I was confident with the drops. It's hard to explain how much more satisfying it is to see what you want to know as colour rather than as numbers. It feels more connected to the plant. If you've already got a meter and most people have, I would urge anyone to get a bottle of the indicator drops for ten bucks and use it side by side for a while. You have nothing to lose.
gro-tek is dark brown like mud.
I never got mould in my calibration solution but I did get algae.
if you store it in a dark place it stops the algea.


Kia ora. Retired to watch the grass grow.
Staff member
AFN Global Moderator
Cultivators Club
Sep 15, 2016
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Currently Smoking
Dabs of Rosin.
I need to check the PH of my reservoir a minimum of 3 times a day and I often check 4 or 5 times. I would be dipping an mixing for way too much time. My Blue Lab comb meter lives in the reservoir 24/7/30 then is re-calibrated and put back in the res. for another 24/7/30. I touch a button and I know where the PH is to within +- 0.1 It really does not get more accurate or easier than that.

The Iconoclast

Auto Warrior
Oct 6, 2018
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@Mañ'O'Green, sure I get it, it's not more nor less accurate, it's really a matter of preference. I just like to dispel the myth that it's anything to do with accuracy. Even my $7 original pH pen was so accurate that I could calibrate it at 6.86 and it was exactly spot on with the 4 buffer.

Pen or Ph they are both perfectly accurate. Doing the drops is a little bit more fussy. You pay a little bit extra for the drops both in time and the actual cost of the solution. The pH pen if for those who like fresh coffee, but they buy it pre ground, the indicator drops are for those who like to grind their own by hand.

TL ; DR, both are accurate, drops is a bit more close and personal, one is a digital readout the other is an intuitive colour. Take your pick. However for me the biggest actual practical advantage of the drops, is that because I do get unexpected fluctuations, I have the peace of mind of not needing to ever wonder if my pen is out of calibration or just gave a wrong reading and then I adjusted for it, that peace of mind is worth a lot to me.