hoppycalif

I ended this test today, and was shocked by what I found: the Rotalas in the STS substrate had much bigger roots than those in the pool filter sand. The difference is about a factor of 4. No wonder the STS Rotalas grew so much better. The Hydrocotyl plants didn't have nearly that big a difference in roots, but the one in the STS was a bit bigger root mass.

This can be caused by at least 2 diffferent things: One, the STS has larger particles, so there may be more room for roots. Second, the STS high CEC may encourage root growth. A way to determine which of the two is more likely is to use a sieve to remove the fine particles in the sand, leaving roughly the same particle size as the STS. If the plants then grow about the same as in the STS it might just be the particle size making the difference. But, I'm not going to do that, for now. I have another test to do first.

Next, I am going to see if API CO2 Booster results in better plant growth. https://www.aquaticplantcentral.com/...ml#post1012593

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davemonkey

Thanks for posting the results, and for doing the trial in the first place. This experiment was informative and useful for the hobby!

mistergreen

STS - 1
sand - 0

Seattle_Aquarist

Hi @hoppycalif

Good experiment and the results don't surprise me. Along with the higher CEC in STS (verses zero CEC in sand) and other calcined clay substrates they also contain large amounts of micro-nutrients (and potassium) which are relatively easy for plant roots to access and utilize. Here is a table that was part of an article in Planted Aquaria Magazine (PAM) Summer 2000 issue. Look at the CEC and nutrient levels of the various calcined clay materials (#8, #16, #16a, #17) verses Flourite (#19) or sand (#21). -Roy

Reprinted from Planted Aquaria Magazine (PAM) Issue #2 Summer 2000

hoppycalif

Roy, that is a great table to keep in our brains! I don't recall ever seeing it before.

Maybe plants grow lots of roots when there are lots of nutrients available to the roots, but only a few anchorage roots when there aren't lots of nutrients?

davemonkey

I would think compaction would have an impact as well (sand is more "compact" than STS, for example). In a farming situation, crops will develop deeper and more robust roots in soil that has been minimally tilled (which means less heavy equipment traffic and less disturbance of soil structures) than in conventional settings, even in the same soil series (same nutrient load). Soil Heath scientists have found that the less disturbed a soil is, the more air space/pore space exists, which translates into larger root mass.

hoppycalif

That would be my first guess on why the root masses were so different. Maybe my next experiment will be sand with the "fines" removed vs. regular sand. I have almost a full bag of sand left over so it would be fairly easy to do. And, that might make the sand more like gravel - less compacted.

mistergreen

Would STS make a good filter media or do they break down overtime?

hoppycalif

Filters are not supposed to change the parameters of the liquid being filtered. They are supposed to remove particles. If you run water through STS, as a filter media, it will probably drop the pH and KH of the water as it goes through. In addition, it would shed very fine particles which would end up in the "filtered" liquid. I doubt that using it as a filter media would be anything worth doing.