Brown layers on plant leaves / Diatoms
My friend has an aquarium in which there are several brown spots on the plant leaves. They can easily be removed by rubbing. It would be nice if you could tell me what this is.
according to the description, they are very likely diatoms. The layers should feel like sandpaper in that case.
Diatoms are pioneering organisms in newly set-up aquariums, usually they become less after a short while.
If the aquarium has already been in operation for a longer time you should first try to deal with the problem by strict nutrient control, i.e.
* reducing the number of fish/the food amount
* abundant addition of fast growing plants
* generous partial water changes with water low in nitrate and phosphate (!)
* possibly installing a nitrate removing slow flux filter
* not using care products that contain nitrate and phosphate
* constantly low nitrate and phosphate levels, but not "zero" mg/l. Nitrate should be about 5 - 10 mg/l, phosphate about 0,1 mg/l.
* creating optimal growth conditions for plants (good lighting, possibly CO2 fertilization, suitable bottom gravel, etc.)
Some patience is required, it may take several weeks before a visible effect takes place.
Some fish and snails also readily eat diatoms.
If that does not lead to success, it is unfortunately necessary to remove the silicate from the water (→ use deionized water, i.e. by reverse osmosis or an ion exchanger). Background: These algae imperatively require silicate to live. They use it for building their hard shells; therfore the layers feel rough when stroking them, similar to sandpaper (see above, please).
Silicate is not removed from the drinking water - it is not toxic -, but is sometimes even added on purpose for preventing corrosion.
Dr. Bodo Schnell