My 2-3 month experience with Green Dust Algae


New Member
Apr 24, 2023
Hi All,
First time posting. (From Sydney,Australia) I hope I can help contribute even partly as much as I’ve learned from this forum. I have 4x planted tanks with all different levels of plants etc + shrimps and nano fish. Love aquascaping and keeping a stable thriving environment (as much as possible lol)
FWIW I wanted to share my experience in being smashed with green dust algae and what I found overcame it.
Please note that I have definitely made some simple errors that were very beginnerish lol. I’m not a pro, not even highly experienced but just keep learning from my many errors and some successes.

TLDR algae went away after improving/increasing siphoning substrate, increased co2 and increasing ferts to at least a minimum required amount. Reduced light but plants not happy so increased to original setting, this improved plant health/growth. Algae still lingered after being cleaned and then used hydrogen peroxide to finish it off for good. Hopefully lol

details of green algae tank:
- 100L (26 gal)
- 120cmx30x30 (48”x12x12)
- Fluval stratum + ada v2 substrate (12 months old)
- Co2 injection (4 b/s co2 art reg, lime green dc) approx 1 point ph drop or more? (API test) starts 3 hours before lights on, until lights off.
- aquario neo diffuser/mixer in outlet)
- Chihiros slim 120cm currently at 80R/35G/65B 6 hours (no ramp time)
- biomaster 250, surf. Skim, internal 200w heater
- LCA all in one EI dosing (use much more than stated on bottle to maintain nitrates at approx 5-8ppm.
- LCA Root tabs (1 ea week to keep levels moderately stable).
Nitrates tested near daily recently showing approx 5ppm (dose up to around 10ppm ea day)
Phosphates approx 0.4 dosed up to approx 1.0 ea day)

I’m not sure how my tank is chewing up so much nutrients? Substrate is quite old now though and tank has no hard scape and ‘full’ of mostly fast growing plants: many varieties of Rotala & Ludwigia + flamingo crypts, AR, S Repens ets etc approx 20 different species all up. Probably too many lol. But all growing surprisingly well now.

Green dust algae first started after putting in 4x varieties of plants purchased online. I noticed one type had some greenish look on leaves but still put it in ( see what happens lol). Well what happened is within a week the gda started covering parts of the glass and within another week basically covered the whole surface of the glass on all 4 panels. I wiped clean and was halfway back after 24 hours and full of it again after 48 hours! Kept cleaning twice a week but nothing changed for 2 weeks.
I’m freaking out at this stage, no other clear algae issues apart from the gda, then it started to cover my leaves of various stem plants.
What I tried:
- First I reduced light by 10%, plants growth similar, lost a bit of colour, and gda carried on happily.
- 1 week reduced another 10% plant growth suffered a bit, leaves looking a bit sad. Gda kept loving life.
- Increased co2 from 3bs to 4bs gradually over another week. Mountain minnows still playing happily, cherry shrimp didn’t care. Had good surface agitation. Nice ripple along the tank surface but not breaking the surface.
- plants started lookin a bit better even with the less light but not as good colours as I expected.
- increased light back to normal and begin checking nitrates each day…. and found a problem.
- nitrates showing yellow on api test. I thought would have had plenty, as I was following the instructions on bottle reading: all in one ei dosing, 3x pumps @ 3 times a week for a weekly total of 24ppm nitrates, 6ppm phospates and 20ppm potassium + all micros (iron 1.5ppm weekly). Also bought another nitrate test kit and same result)
- how could it be so low? I did near double plant mass in 1 day but itstill surprised me (inexperience showing lol). I started dosing 1.5 times more the weekly dose (started putting 2 pumps per day /14 per week instead of 9 per week).
- nitrates better but still near yellow on api test. Below 5ppm. Started to do 3 pumps per day and this had it at around 5ppm before ea daily dosing. This is equating to approx 40ppm nitrates being dosed each week. I don’t understand but this is what the tests are showing me. Also add LCA gh additive weekly
- started doing larger water changes each week at 50-60% instead of 30-40%.
- increased light back to to original settings and plants exploding with awesome growth, topped stems that reached surface periodically and slowly increased the super healthy percentage of plant mass. Even the macrandra is finally looking good lol.
- gda still there but slowly slowly started to see some fainter areas on the glass.
- a couple more weeks went by and still very slowly seemed to be fading or stalling I couldn’t really tell?
- gave up not cleaning the glass (I couldn’t look at it anymore!) and gave it a 80% water change and cleaned surface with paper towel and wiped with hydrogen peroxide.
- this hit it hard but the parts I missed slowly started spreading back again. Plant growth still awesome though. Added seachem stability to help out after using the hyd. Peroxide
- after another week cleaned again with hydrogen peroxide at water change and also added 50ml to tank. Same result as week before though it started to slowly come back. No other algae visible, only the gda.
- repeated the same again the next week but this time dosed 100ml (high dose I know, but fish/shrimp were in a bucket, plants showed no distress) but algae was hit hard but still showing up by the end of the week but much much less however still growing slowly.
- I didn’t know what to do at this point, it was growing back in some areas but others were sort of getting fainter afterwards?.
- same treatment another week later, 80% water change, thourough glass cleaning, removed any broken down soil/detritus from substrate. Cleanest I’ve ever seen the soil during the last 6-8 weeks, although I siphon it each week any way, I even got the turkey baster as part of the weekly maintenance (cheers Dennis) hoses, filter, diffuser and pipes cleaned every 2-3 months as needed. Prefilter maybe every 2 weeks rinsed out.
-at the end of this water change I dosed 150ml of 3% hydrogen peroxide ( no fauna in tank). This wiped the dust algae out. Plants didn’t show any problems only one stem tip a bit melted (snipped it off). No gda for 2-3 weeks now! And tank is exploding with growth and colour.
-also forgot to add that I added purigen and filter floss in a small hob to help clear out anything in the water column, maybe helped! Not sure. But it’s gone!
Cheers guys.
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