Normally appears on glass (as in the picture) and slow growing plant leaves such as anubias sp. Relatively easy to overcome by scraping glass with a suitable flat edged piece of plastic (scraper is sold in LFS or use expired credit card etc.) and removing affected leaves. Indicates a deficiency of Phosphates. Dose with Monopotassium Phosphate (KH2PO4) or other suitable sources of P to prevent recurrence.

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