Unfortunately, I got so disgusted with it that I completely emptied the tank. But, toward the last few days, it was spreading out like a carpet of brown algae on the surface of the sand substrate, totally obscuring the sand underneath, it also formed on the 4" diameter rocks, and adhered to the plant surfaces. It was going wild!
But, because it was growing on the top surfaces, on the sand, the top edges of the Rocks, etc...I am beginning to wonder if lighting might have been more of a contributing issue than I thought. Unfortunately, I don't have any photos of it. My motivation was to get rid of it so I could start over.
I moved the fish over from the 20 gallon Brown Algae tank to an empty 10 gallon tank, used synthetic black gravel from Petco, a couple of fake silk plants, etc...And, that was two weeks ago, and so far NO brown algae yet.
Another thing I did was to switch the lighting to a spare Marineland "Double Bright" LED light fixture I had, thinking that maybe insufficient lighting was a contributing issue. I had been using three 5 watt CFLs in a home-made rain gutter housing on the 20 gallon Brown Algae tank. Before that, during a time that I seemed to have less of a problem with Brown Algae (slower growing, but still there), I had been using an LED strip light that I built. The PAR reading with both the CFL light, and the LED strip light, was around 8-15 micromoles at the substrate.
Now, using the Marineland fixture, PAR measures about 20 micromoles on the 10 gallon tank at the substrate. So, the light levels would still be considered a relatively low level, but theoretically sufficient for appearance sake. But, not generally considered sufficient to raise plants that need anything more than very low levels of light.
I think that the low intensity lighting, the high silicate substrate, too many plant root tabs, the silicate content of the rocks, the silicate content of my hard water, etc...all contribute together to exacerbate their effect upon the problem. So, it may take more of a holistic approach to resolve the issue. But, I do theorize that one element of the whole issue is probably the sand substrate, as well as leaching of silicates from the rocks and water.
So, I'm hoping to use the best choice of substrate when I rebuild the tank, to possibly mitigate any contribution that substrate might make to high silicates that might be causing the brown algae issue. If I stick with the Flourite, I might try to sift out the sand, and separate it from the Flourite by using a screen and a bucket. It could be that salvaging my Flourite as a substrate, and totally eliminating the sand and rocks, using fewer or even no root tabs, supplementing plant nutrition with water based additives like Seachem's Flourish or something, might be the right approach. I also plan to build a better LED light fixture with controller, one that has the right number of LEDs with the proper color temperature capable of delivering optimum PAR.
With respect to high silicates, I can't change the hard water-high silicate water condition beyond what I'm doing with respect to running the soft water system. So, I am focusing on the things I can change.
If I'm planning to plant rooting plants, I'll need a substrate that permits good rooting action. It would seem to me that in order to plant rooting plants, the substrate would need to be a smaller gravel size than the Flourite, which I could reuse if I salvage it by separating it from the sand. But, I don't know if Flourite is adequate for planting rooting plants with respect to the size of the gravel, or if there's a better choice, taking the potential for high silicates contributing to the Brown Algae into consideration as well.
In my case, considering the hard water and high silicate content, I kind of think that a totally synthetic substrate might be answer to the higher silicate component to my water quality, but the synthetic gravel is too large for rooting action. So, if anybody knows of a synthetic substrate that will sustain plants, one that's about half the diameter of the Flourite, I think it would fit the bill nicely.
I think that having too many root tabs is a really likely cause for high nitrites and high silicates, which feeds brown and green algae both. So, if you can remove them easily without completely rebuilding your tank, I would try that, and feed plant nutrients with Flourish or something similar. In my case, I had to completely remove the substrate because of the sand (high in silicates), which caps the Flourite. My tabs were buried in the substrate, and couldn't be easily removed without completely removing the entire substrate.
If we can get a handle on the nitrites and silicates introduced via the substrate and the root tabs, I think we'll be on the right path to solving this issue. Any changes made to the substrate just helps mitigate the further detrimental effects of the silicates induced by hard water quality, and/or the high nitrites resulting from having an excessive number of root tabs. Lighting is the third rail.
I have the same problem with brown algae attacking my substrate... It has happened to my tank after tearing it down as well. I had eco complete over a MGOCPM cap at first that lost the battle very badly and now I still get the stuff with black diamond blasting sand with a bunch of osmocote tabs buried in it. Really hurts the growth of my hair grass and it even gets on some of the lower leaves of my healthier stems. It suffocates a good amount of my hairgrass - really only the newer growth is able to avoid it.
A part of me things that I have too many nutrients buried in the substrate - first with the dirt and now with the osmocote pellets. Who knows though - another part of me things there are other factors at play.
I only get this in my high tech tank. My low tech tank has no traces of it.
Honestly I'm not sure switching substrate will save you... It certainly didn't save me.
do you have pictures of what yours looks like? I will take some tonight to see if it is similar to what I deal with.