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Green spot wont stop


7 Jan 2013
Hey all.

Touch wood my aquarium is currently pretty algae free apart from green spot which I cant seem to shift.

Going on Jame's planted guide seems it could be low co2, low phosphate, poor water flow, to long a photo period or a combination of them.

my tank is 200l

I think I have flow sorted. I have a full length spray bar running off two filters and a power head. I can see good plant movement in all parts of the tank.

Lighting is from 2 30w T8 tubes on for six hours a day.

injected co2 on for 6 hours a day, comes on 3 hours before lights and drop checker is bright yellow at lights on. I cant inject any more co2 at all as I'm right at the limits for the fish.

This leaves me with phosphate. I'm EI dosing and have been using the recommended mix from aquarium plant food.
on my last mix I tried adding more potassium phosphate "recommended was 1tsp, I used 6tsp"
but It didn't seem to help with the green spot algae.

Is there any thing else I should try?
Do you think I need to add more potassium phosphate? It seems like a lot?

cheers for any help.
Dan, just because you are at the CO2 limit for your fish, it does not mean that poor CO2 is not the cause. The only other direction to go in is to supplement with liquid carbon or to reduce the light intensity, at least temporarily.

cheers for the replies guys.

Forgot to mention that i'm also dosing glut, 10m per day. I could up the dosage as I was dosing 20m per day but I went down to 10 a few weeks ago as I think the glut was killing my weeping moss? I had the green algae before this change though and dosing more didnt seem to shift it.

The lights are fixed in the hood of the tank so I cant easily adjust light intensity but I can lower the photo period. maybe drop it back to 5 hours a day?

filters are cleaned every 3 months or so but I only run bio rings in them.
I had this problem. I upped my overall EI dose regarding all macronutrients, reduced light (then gradually increased over time) whilst injecting CO2 at a stable 30ppm alongside liquid carbon.

Best of luck,
Floating plants or upside-down reflectors are a couple of ways to reduce the intensity.