05-12-2013, 05:47 PM
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That is a type of brush algae, according to George Booth and others. Below is a pic from him. Brush algae can take many forms.
It is caused by light being greater than the nutrient balance. The nutrient balance itself can also affect it. Recently, the Echinodorus bleherae in my 90g became covered with this in a matter of days; it was so sudden I didn't really notice it building, until I realized every sword leaf was being encrusted. For reasons I won';t go into here, I suspected in this instance that nutrients were the issue and I reduced the liquid fertilizer from twice to once weekly. [I use Flourish Comprehensive Supplement, and had been dosing twice a week for several months.] Within less than 2 weeks, it was gone, which is to say, it never increased on new leaves. I removed the older encrusted leaves week by week to tidy things up.
The balance is obviously out, either within the nutrients themselves, or involving the light, or both. You are using dry ferts, of which I have no experience. But KNO3 is potassium sulfate, KH2PO4 is potassium dihydrate phosphate. Where are all the trace elements coming from? I did another experiment, reducing Flourish Comprehensive from twice to once weekly in my other tanks and adding Flourish Trace once weekly. This has made another improvement. From both of my experiences relayed here, I would say that macro nutrients were being overdosed.