# GSA and GDA: What's the difference?



## Nevermore (Mar 26, 2007)

Is this true?


Hoppy said:


> Green dust algae is a soft film algae that usually grows on the glass, but can easily be wiped off. Its spores are "zoospores" early in its life cycle, which are free swimming spores. When you wipe the glass the spores swim around and resettle on the glass to resume their life.
> 
> Green spot algae is a hard algae that grows on the glass and any other non actively growing surface. It forms small circular spots. It scrapes off, but only with effort.


I've been thinking I had GDA but I would never say it "wipes off". I have to scrub it. It looks like a fine dusting all over my glass. When I rub my fingers over it, I feel tiny bumps.

Strange that it could be GSA because I tested my phosphates about two weeks ago and it was 2 ppm.

I hope it is GSA, can anyone confirm?


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## trenac (Jul 16, 2004)

Sounds like GSA from your description. Could be that you test kit is off. _What is your nitrate reading_?


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## Nevermore (Mar 26, 2007)

My nitrate is 13 ppm. I'm using the LaMotte test kits for both nitrate and phosphate testing and their kits are usually supposed to be fairly reliable. Maybe I should test the test kit just to be sure.


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## trenac (Jul 16, 2004)

If you get the same readings when retesting I would still try increasing the P04 dosing to see what happens.


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