dwalstad

Hello APC Folks,

Here's a question I just received:

"Over the last several months the plants in my tank have stopped growing and leaves are starting to yellow and die. Up till that point plant growth was quite good. I have 100% fluorite as a substrate, and I'm wondering if the effectiveness of fluorite declines over time. I've had it for about 6 years, 2-3 inches in a 75 gallon tank. Have you any info about
fluorite? It was not addressed explicitly in your book." (from Maryland hobbyist).


My response: It could be allelopathy, which is the plant root release of inhibitory chemicals. These "allelochemicals" can build up in the substrate over time. I discuss this in my book (see Q&As on pp 48 and 51).

Another possibility is that the substrate organic matter degraded to the point where it is no longer releasing enough CO2 for plants. However, fluorite doesn't have much organic matter to begin with, so I don't think it would be the gradual dropoff in CO2 release one sees sometimes with potting soil substrates.

Since aquariums are generally overrun with nutrients (CO2 is usually the limiting nutrient), I suspect that the drop-off in plant growth this hobbyist observed is due to the build-up of something inhibitory. Allelochemicals, heavy metal precipitates, etc?

Again folks, just because a soil comes in an expensive package doesn't guarantee that it will perform any better than a shovelful of garden soil or a bag of inexpensive potting soil.

bencozzy

flourite is nothing more then a hard laterite clay.

and laterite can loss its zing in about 2-3 years, thats not saying its lost all its iron ore in it. im just saying ive observed plants tend to slow down at about that time when your using laterite.

usually dosing potassium and iron help with that type of thing.

as a side note im using your method in a emmersed culture set up on crypts and ive been noticing some decent growth.

ben

Robert Hudson

Actually there is a difference between laterite and clay if you want to get really technical. Flourite is baked clay. Clay and laterite provide oxidized iron, and its inert, so basically it lasts forever. I don't see how it could get depleted. Flourite does not provide any macros at all. If he is releying soley on Flourite, where are the macros coming from? I think you are right Diana, there would not be any organic material in his substate other than fish waste and decaying plant litter. His plants are probably starved for nitrogen