What's promoting my algae? - The Planted Tank Forum
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post #1 of 3 (permalink) Old 01-09-2021, 01:28 AM Thread Starter
Algae Grower
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Location: Saint Paul, MN, USA
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What's promoting my algae?

So, about 2.5 months ago I redid a 42 gal tank. I'm headed down the same road with stag-horn algae as I previously had, and it wiped out my plants. Everything gone. However that's not why I took the tank apart. I ended up with a drain-line issue on my overflow and had to rework the plumbing. But the return of the staghorn algae and the prospect of losing it all again is frustrating. I am keeping it in check right now with targeted H2O2 hits after water changes. But I know I need to figure out what about my conditions is favoring the growth of this pest. This time I am also getting luxurious green algal growth, which is less concerning to me, but may still help with the puzzle. I'm hoping if I list what I have going people can point out where I have gone awry. Thanks in advance!

-Tank components-
Low tech tank - no CO2 supplementation

Lights: cheap NICREW LED strip with white, red, blue and dimming running for 8 hours a day (no direct sunlight on tank)

Stock: 40+ N-class Endlers, 10-20 cherry shrimp, various pond snails
Flora: loads of Cabomba, small tiger water lily, 10 dwarf sagittaria, 4 Isotes, 2 large Anubias, 2 congo ferns, few Salvinia minima, 1 mat of buce, + some java moss around
Hardscape: Malaysian bogwood, "bluestone" from a local rockyard
Substrate: Seachem Flourite Black
Filtration: wet/dry sump rated to 150gal with biohome in the top and pumice below

-Water Parameters-
Temp: 23-24C
pH: 8.2
TDS: 120-130
Ammonia*: 0ppm
Nitrite*: 0ppm
Nitrate*: 0ppm
Phosphates*: 0-5ppm
GH*: 6

KH*: 4

Grain hardness: 7

*API test kit results FWIW.

If I have forgotten something let me know. Thanks in advance for any help.
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post #2 of 3 (permalink) Old 01-09-2021, 10:26 AM
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What's promoting your algae? Unhealthy plants!

Give plants what they need and they will help you kill algae. You mentioned nitrate NO3 is 0 ppm, that’s no good. Plants must have source of nitrogen N in order to grow, give them KNO3. Then you posted phosphate PO4 at 0 – 5 ppm, what is it? Zero or 5 ppm? Plants need phosphorus P to stay healthy. You need to give them KH2PO4. These two plant nutrients are usually supplied with fish waste so make sure the test kits are working correctly. But plants need more than P and N, please see here and here.
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Last edited by Edward; 01-09-2021 at 10:28 AM. Reason: .
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post #3 of 3 (permalink) Old 01-09-2021, 02:01 PM Thread Starter
Algae Grower
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Hi Edward. I certainly have created highly oligitrophic conditions in my system. Interestingly, I had similar values before my plumbing issue but the plant growth was luxurious for the first few months. I suppose I presumed the new substrate, which was the same from the earlier round, would provide some of the nutrients the plants would need (if not why did I pay so much for this stuff when sand would have worked better from a particle size perspective?!). I've got fert tablets. I'll give it a go. Thanks.

In terms of your question about my reported phosphate levels, it's an API color matching test. The color is a shade between 0ppm on the chart and the 5ppm color provided on the chart. You seem quite experienced, so I wouldn't have expected this to take you by surprise. Hopefully this explanation helps alleviate your confusion in my reporting.
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