Test Strips GH Reading?

[Amorak]

Just received my Aquarium co-op Test strips last night. Tested my water and all of the test results agreed with my API Master, GH/KH, Chlorine test kits - except the GH. The color on the GH looked magenta (more red) than any of the colors on the chart. After about 5-10 minutes it looked like the edges of the pad were starting to change to a more correct color (at this point pH, KH were no longer even close).

My API kit measures my GH at 196.6 ppm (11 drops).

I did the 3 second swirl and 1 minute lay flat - on the bottle as shown in the picture.

[Baphijmm]

Where was it laying flat? I tend to hold mine in the air, just horizontal, for the full 60 seconds. If I set it down anywhere, I find the test picks up stuff on that surface. I've even gotten cross-contamination just measuring against the bottle, from testing multiple tanks. They're surprisingly sensitive.

[PaigeIs]

I have the same issue with the Aquarium Coop test strips.  My GH reading is ALWAYS a dark pink rather than purple.  I use test strips for weekly checks and my API test kit on a monthly basis. The water where I live is very hard so rather than worry about color matching, I use the test strip reading to confirm that nothing has changed. In my case, a GH around 250.  I've tested the strips in bottled water vs my tap water to verify that the strips "work."

Edited May 18, 2022 by PaigeIs

[Cory]

The pink/purple shade indicates over 300 ppm of hardness on our strips. We had that confirmed with the lab. I'd have to look it up, but a chemical in the water can also do this but it wasn't common.

[nabokovfan87]

I saw this video, link below, the recommendation being when you lay them flat, put them on a towel to avoid one of the pads mixing results with another pad.

This provides a bit more "clear" result than something like sitting it on a surface that doesn't absorb water.
 

 

[Torrey]

I have had the experience Baphijmm has had: so sensitive I can skew results if I'm not careful. I'm typically testing 6 to 13 tanks at a time, so I lay a paper towel on my "fish tank cutting board" and walk through doing the 3 second swirl and laying flat on the paper towel.

By the time I get to the end, my first strip has hit the 60 second mark, and I start reading the strips.

Most of my tanks were well over 600 TDS back in January (water comes from an aquifer, and so much calcium it causes kidney stones. I mix distilled or ZeroWater with Pur filtered tap water until I get 180 TDS... but accidentally dropped my KH, so still testing water religiously until I get this balanced)

My GH was a magenta purple when I got my strips in the beginning of April. Weekly water changes is slowly lowering the GH, and this week I have 2 tanks down to a perfectly matched 150 GH ppm. My ZeroWater tests at 0 ppm for both GH & KH, and our treatment facility has changed something, bcause last October (when I ran out of strips and reverted to exclusively using the API liquid reagents) my Pur water out of the tap had 300+ GH  and between 120 & 180 KH ppm.

Now, the Pur doesn't even have 40 ppm KH, and out of the tap is between 40 and 80 ppm KH. But the GH is still through the roof, and TDS out of the tap is well over 400 now, and down to 280 TDS out of the Pur faucet filter.

A friend works at the Labs, and periodically gets permission to test local water samples. My strips and my API tests have been within acceptable parameters/deviations when tested against the labe (not as precise, but correct in the "between this and this" parameters). It is absolutely critical to get the strips horizontal immediately. I like laying on the paper towel, so no drops of water move between the pads, skewing the test.

Worth the extra attention to detail so I don't have to shake a test tube or reagent bottles until my arm falls off, lol 

[Amorak]

On 5/17/2022 at 10:17 PM, Baphijmm said:

Where was it laying flat? I tend to hold mine in the air, just horizontal, for the full 60 seconds. If I set it down anywhere, I find the test picks up stuff on that surface. I've even gotten cross-contamination just measuring against the bottle, from testing multiple tanks. They're surprisingly sensitive.

It was laying horizontal on the side of the container as shown in the picture.

I'll try laying out on paper towel next time.

Thanks,

DJL

[Brian]

This made test my water and test the test strips. I purchased mine March 21, 2021.   And mine are still reading/working just fine.  
Nitrate between 25-50

Nitrites 0

Hardness 150

Buffer 40

PH 7.2

Chlorine 0

Out of 6 tanks all is about the same with three exceptions:  planted tanks reading 0 on Nitrates.   Time for some easy green I guess.

 Thanks again Co Op family for EZ fish keeping.    

[Brian]

Also, I would think some readings will change/differ based on when you test.  Right after a feeding, water change or filter maintenance?  @Cory care to weigh in on this?  Any way I just used my three Easy Fertilizers and the only change I got after 45 minutes was my nitrates.  

[Cory]

I'm not sure how long it takes to fully mix different compounds into water. For instance feeding, you'd need the fish to release urea, and do they release enough to be measurable that early? With easy green, the testing time should be the amount of time it takes to adequately dilute into the water. I honestly don't know this. I would think in the average aquarium it'd be less than an hour. But I can see  sponge filter in a 55 gallon taking longer than say a canister filter. But that is purely guessing.

[jwcarlson]

My water is hard as heck and the GH pad turns purple/pink.  I'm not particularly worried about GH as it should be pretty consistent in my tap water.  If you want/need to know the number, there's a GH/KH test kit from API that you can buy.  I think my GH and KH tested at 20 degrees each... which is a lot of drops out of the bottle! 😄