# Light + low Potassium = algae again



## ecotanker (Jul 11, 2009)

From my experience, BGA is a sign of low nitrate. You may want to add more fish food or nitrate to see if it with help.


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## Django (Jun 13, 2012)

Sorry, my nitrates are 40 ppm, lucky I'm going to do a big water change. I think you may have got it a little backwards. Thanks for the reply.


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## Hoppy (Dec 24, 2005)

Most of us use KNO3 as our source of both potassium and nitrates. When we see BGA we add more KNO3 and it usually helps a lot. That could be from the potassium or from the nitrates. If you want to test whether it is potassium that helps, just dose K2SO4 instead of more KNO3. If that knocks out the BGA it is possible that it is the potassium that does it, but if it doesn't affect it, it is unlikely that it is the potassium.


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## micheljq (Oct 24, 2012)

In my case BGA disappeared one month after I began dosing nitrates and phosphates.

Nitrates alone did not help in my case, with or without potassium.

Michel.


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## csf (Jul 10, 2003)

The usual EI dosing mantra is "if you have algae, check your CO2 and your phosphate, one or both isn't high enough for your light. Backup plan, lower light brightness".

Seems to be consistent w/ other notes here.


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## Low_t Tom (Jan 23, 2013)

I thought phosphate was a bad thing in aquariums?

http://www.skepticalaquarist.com/phosphate-cycle


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## TexasCichlid (Jul 12, 2011)

Phosphates causing algae is a myth perpetuated by the clueless.


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## Django (Jun 13, 2012)

I'm a ferts newbie. Think I should dose the whole NPK? I have pinholes on the leaves of an unknown plant and my old Sword leaves are symptomatic of something else. Does dosing NPK hurt at all? Thanks, and thanks for the replies.

Steven


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## micheljq (Oct 24, 2012)

Low_t Tom said:


> I thought phosphate was a bad thing in aquariums?


There are algae free aquariums with high nitrates, there are algae free aquariums with high phosphates.

Phosphate is an important macro for plants. From my personal experience, the most important algae issues i had was when I had 0 phosphates and not dosing phosphates at all.

Michel.


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## acitydweller (Dec 28, 2011)

And here i always throught bga came by way of infected palnts as hitchhikers...


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## farrenator (May 11, 2011)

I don't know the answer to your lighting question. As to the other issues, it is time to define terms:

By BGA most people on this forum refer to cyanobacteria - forms a dark green slime/skin on the substrate/plants that is easy to peal off. People report its appearance in low Nitrate situations as stated.

GDA - this is also green and appears in the beginning as small dots/spots on the glass - it is easily removed with a scraper but quickly reappears. I have had this when I had too much light. Reduce photoperiod and/or intensity (# of bulbs/height of light above tank)

GSA - also green in appearance but much harder to scrape off. You will often find it on the glass or leaves of slow growing plants such as anubias. I have cured this by adding more phosphates.

Not sure which algae you have but these are some general approaches to take.


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## csf (Jul 10, 2003)

The EI dosing method (estimative index) mantra is basically:



Make sure all nutrients are present is easily sufficient quantities. Add more if you aren't sure. NPK, traces.
Make sure you have enough CO2. Low CO2 causes 95% of algae issues.
Make sure you have a proper amount of light. Too low and too high can both cause issues.
The dosing for EI is NPK + trace on a semi daily basis to ensure nothing is limiting plus KH and GH once a week for Ca, Mg and to keep the pH / CO2 relationship in proper order.


Then do a weekly water change to make keep any one thing from getting too high (fish fatal). Note - there is a large margin of error before fish start being impacted in my personal experience. I've slipped on WCs to every 2nd or 3rd week on some occasions and fish have been fine.



The "low phosphate prevents algae" is antiquated, old school. Plants need all 3 macros to grow well, don't limit them. Trim out algae when you see it, get some algae snacking denizens, and then let your plants out-compete your algae.


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## micheljq (Oct 24, 2012)

csf said:


> The "low phosphate prevents algae" is antiquated, old school. Plants need all 3 macros to grow well, don't limit them.


Totally agree :red_mouth

I think that we cannot starve algae, but we can starve plants.


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