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JohnLW 11-21-2013 01:09 AM

Does Flourite increase tank GH?
I have been measuring water parameters as my new fresh water aquarium (20 gal.) has gone through cycling and population with plants and fish. I wanted good plant growth and invested in a bag of Flourite which I topped with previously used aquarium gravel. I washed both well before putting them in the new tank. The intial readings were GH - 9 and KH - 4. In two weeks the GH was up to 13 and dropped to 12 after I replace 10% of the tank's water. KH, pH, NH3, NO2 and NO3 are all stable and at reasonable values. The fish and plants are happy but I worry about the increasing general hardness. What is a reasonable GH range for tetras and corys? I suppose I could change out water more than once per week or even mix in some softer water, although I am about to try DIY CO2 and don't want the KH level to decrease much. Any thoughts?

Texan78 11-21-2013 04:21 AM

I am currently using Flourite in my 50G which has been running for a week and I haven't seen an increase in GH but, I am also running CO2. I am due for a 10% WC Friday and will check it again then when I do the change verus what it is at before it and 24 hrs later and see what I is running.

Wannaberooted 11-21-2013 05:16 AM

No, I believe it is inert. It has high cationic exchange capacity, that's it.

Subtletanks91 11-21-2013 05:53 AM


Originally Posted by Wannaberooted (Post 4718681)
No, I believe it is inert. It has high cationic exchange capacity, that's it.

What does this mean haha. Every time I come on this website after work an in the morning when I am feeding my daughter I feel like I'm in college going to biology, marine courses, and studying aquatic Eco system behavior and bacteria/algae course 101.

Always something new.

Darkblade48 11-21-2013 06:46 AM


Originally Posted by Wannaberooted (Post 4718681)
No, I believe it is inert. It has high cationic exchange capacity, that's it.


Originally Posted by Subtletanks91 (Post 4718809)
What does this mean haha.

Cation Exchange Capacity (CEC) is essentially the ability for a soil to hold onto cations (positively charged molecules). A higher CEC generally means that the the soil is more fertile, as it has cations that can be used by plants.

Wannaberooted 11-21-2013 06:50 AM

Well it does take a lot of reading. It means that it absorbs nutrients easily and releases them when needed if available, but releases no nutrients of it's own despite all the stuff on the label.

acitydweller 11-21-2013 01:03 PM

i've witnessed gh and kh drops with Safe-t-sorb substrate.

Seattle_Aquarist 11-21-2013 01:45 PM


No, I believe it is inert. It has high cationic exchange capacity, that's it.
Hi All,

Just a quick clarification; Flourite (#19) (CEC = 1.7) does not have a high CEC like the Montmorillonite clay materials such as Turface (#16) (CEC = 29.8-41.1) or Safe-T-Sorb #7941. Although Flourite has a relatively low CEC it does contain a lot of mineral nutrients essential for healthy plant growth; although the low CEC would bring into question the ability of Flourite to release those minerals to plant roots.

CEC Values of Various Substrates and Additives (per Planted Aquaria Magazine issue #2)

micheljq 11-21-2013 04:37 PM

Flourite is not inert, sand is.

JohnLW 11-21-2013 06:39 PM

The table that Roy kindly provided shows that Flourite does contain some Ca and Mg which contribute to GH, but not in high amounts compared with many other substrates. I guess I will just increase water change frequency and hope that my run-away GH tops out and eventually declines.

DarkCobra 11-21-2013 08:55 PM

New Flourite is pretty dusty, and you can never fully wash it all out. The fine dust may be leaching some minerals out. I've not checked GH specifically, but have seen some evidence that new Flourite Black can initially leach out a good bit of manganese.

If this is the case, it should resolve within a week or two.

Wannaberooted 11-22-2013 02:58 AM

I certainly not going to argue with people that have so much more experience than I.

My experience with Flourite has shown me however, that it has not changed my water parameters in any way from my tap water. When I first started with plants, I expected the Flourite to supply the nutrients in a low light tank. All my plants were dying until I started dosing iron and potassium. They didn't start thriving until I put in root tabs.

That was my reasoning to state it is inert, basically.

JohnLW 11-29-2013 05:32 PM

You were right DarkCobra. My tank's GH stopped going up and is now headed back down toward my tap water's GH with water changes. I'm not sure if this was due to the Flourite or something in the old aquarium gravel that sat in a paper bag for 15 years. I had washed the gravel well and it had been previously used in a tank with just plants and fish (no driftwood, etc.). If I ever buy another bag of Flourite, I will hold some out for a test.

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