Strange things are afoot with Flourite

[UntimelyLord]

In my 30 gallon tall, I changed my regular aquarium gravel out with Flourite about five days ago. I've been testing the water every day to look out for a mini-cycle, and so far, so good (ammonia and nitrites at zero) but I seem to have a problem with my pH and KH changing! I chose Flourite as a substrate because it claims to not change pH, and I have an established tank.
All tests with API test tube kits.

Before substrate change: pH 7.8, KH 9 dKH, GH 21 degrees (same as source water)
3 days after substrate change: pH 7.6 (I do not have KH and GH for this as I thought the slight color change was just my eyes seeing things, the color chart is so close, and I also wasn't looking out for a pH change)
4 days after substrate change: pH 7.4, KH 4 dKH, GH 18 degrees
8 hours after 50% water change: pH 7.6, KH 6, GH 20

The substrate change is the only change in the tank. The tank is low light low tech planted.
I found a thread from 2004 in which someone had the same problem. There don't seem to be many cases of this happening, though.
Flourite changes water parameters - General Aquarium Plants Discussions - Aquatic Plant Central
Hopefully more water changes will take care of it. Seems weird, though. I hope it's not possible for the Flourite to "store" KH and then release it back into the tank later, as I've read can happen with some nutrients?

 

[Brookster123]

What was your substrate prior to?

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[UntimelyLord]

What was your substrate prior to?

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Just regular aquarium gravel. Inert.

 

[Brookster123]

Meh.. it's a mystery.. have you tested your water left to sit for 24hrs in a glass??

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[flchamp89]

Not a huge change imo. I wouldn't be concerned.

 

[UntimelyLord]

Meh.. it's a mystery.. have you tested your water left to sit for 24hrs in a glass??

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Yes, it's the same as my "before" tests. Oh well.

 

[Brookster123]

Wouldn't worry about it..latter parameters better suit plants amyways

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[UntimelyLord]

Wouldn't worry about it..latter parameters better suit plants amyways

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Not a huge change imo. I wouldn't be concerned.

Yeah, I'm thinking it won't be a big deal in the long run, just weird. My shrimp were acting less active than usual, I'm guessing they don't like the pH fluctuations but nothing major. I'd be happy for pH and KH to stay down a bit as long as it's stable. I'm not too concerned.

 

[Delapool]

Strange one. If I didn't see the test thread I would of suspected just some stirred up organics which increased bacterial activity and lowered kh / ph.

I swapped over from gravel to gravel plus fluorite. From memory it was pretty stable (although the tank was too cloudy for a few days to do any tests).

 

[UntimelyLord]

Tank is back to 7.4 pH today, 5 KH and 18 GH. I did another water change yesterday, 30% source water (7.8 pH) and it still dropped. Makes me think it would be lower if I hadn't done a WC. Left another cup of source water out for 24 hours to double check that it wasn't fluctuating, but no, it still has the same measurements as my "before" numbers (pH 7.8, KH 9 dKH, GH 21 degrees). Weird.

 

[UntimelyLord]

I swapped over from gravel to gravel plus fluorite. From memory it was pretty stable (although the tank was too cloudy for a few days to do any tests).

I rinsed forever and used extra "water polishing pads" which I had to throw out afterward they were so full of dust. But my water cleared in 12 hours.

 

[Delapool]

I rinsed forever and used extra "water polishing pads" which I had to throw out afterward they were so full of dust. But my water cleared in 12 hours.

I was a bit greedy and wanted to keep as much clay as possible in tank so could of done more rinsing as the filters were pretty bad. It's good now though. I replant stem plants and don't get any clay puffs out of substrate or anything.

I was adding more clay substrate ferts tabs but it's all pretty over-grown now. Seems to be going ok.

 

[UntimelyLord]

Two weeks after substrate change and the pH is still going to 7.4 by 24 hours after water change, despite source water staying at 7.8-7.9 in a glass. Will update when this stops happening!