Cause of my green spot algae - The Planted Tank Forum
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post #1 of 5 (permalink) Old 07-18-2020, 10:10 PM Thread Starter
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Cause of my green spot algae

Hi folks,
I've been trying to work out the root cause of the gsa I get building up on my glass and occasionally leaves. I've got a 200L low tech moderately planted tank with mainly slow growers. I've got a 15w light on for 7 hours a day. My tap water parameters are hard, with zero nitrates and about 5ppm phosphates. I dose excel for a CO2 substitute and easy life for micronutrients. After 2 weeks without a water change my phosphates and nitrates are still comparable to the tap water.

From the other posts I've found on gsa, a low phosphate is often the culprit - I was wondering if a low nitrate could also contribute to it?
Many thanks in advance
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post #2 of 5 (permalink) Old 07-19-2020, 12:00 AM
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I don't know if it causes gsa , but low or no nitrates are not good in a planted tank . Mine stay around 20ppm . I don't add any besides what Easy Green has , and I have floating plants and Pothos growing out of the tank .
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post #3 of 5 (permalink) Old 07-19-2020, 02:14 PM
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I think that you have a macro nutrient problem. I believe that the Easy Life has K (potassium) in it, am I right? If not, you will need to add K. As @Leeatl implied, if your tap has no NO3 and your fauna aren't contributing enough, you need to add NO3 as well. It would also be helpful to know what your GH reading is in the tank, to be sure that you have enough Ca and Mg. Since your PO4 is high, for a low-tech setup (due to your tap), you shouldn't need any additional PO4. Ensuring sufficient NO3 and K (I'm assuming your GH is in a good spot) may be enough to help with plant health and GSA.

Very low PO4 (which is not your case) is often a cause of GSA. However, a low NO3:PO4 ratio can also be a contributor. NO3 should be higher than PO4. I would suggest bringing your NO3 up to about 10ppm.
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post #4 of 5 (permalink) Old 07-19-2020, 03:30 PM Thread Starter
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Ah ok thanks guys. Yeah easy has K in, I'll get hold of some nitrogen to top up with. GH is about 14
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post #5 of 5 (permalink) Old 09-22-2020, 08:29 PM
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Raise your Nitrates, I would test your Phosphates before your weekly water change to see how much it has dropped since the last water change. Ya want your Phosphates to be at 2ppm minimum to stave of the GSA. Depending on your plants, Crypts and Anubias love the potash.

I have no phosphates in my tap, I do a once a week heavy feeding and it raises my phosphates between 5-7 ppm and after 5 days it's at 2 ppm, With my stocking I'm at 30-40 ppm Nitrates. I'm dosing Flourish Potasium at 16ppm a day, I was dosing Easy green, but gonna jump to NilocG S because I don't need the extra Nitrogen and Phosphates.

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