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Help – New tank has me humbled. Brown snot…

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Feb 20, 2026
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HELP!
Returning to the hobby after a couple years break...

By no means a pro… although this isn't my first tank, nor most demanding, yet it is humbling me… hard!
Looking for some recommendations on next steps, I’m starting to come up empty.

Dealing with what on the surface looks like an algae issue, but starting to second guess whether it could be something else?
Could this be a biofilm or fungal issue? The main driftwood piece is quite large and dense, although I'm not seeing biofilm as youd expect concentrated on the wood itself.

I’m struggling with brown, gelatinous looking clumps that are appearing everywhere.
They hang from driftwood, clump in the foreground and take hold in any nook and cranny. It’s completely weaved itself into my moss..

It's almost like a mix of diatoms and string algae, but not quite either.
It’s not filamentous or dark green like you’d expect with string algae, it simply melts into a puddle of brown muck if you try to grasp it…
Some sections of it appear to be pearling oxygen bubbles within it.

I can’t manually remove like you would hair algae.
Sucking it up with a turkey baster helps, but 2-3 days later it’s as bad as it was before.

The overall plant health has not great to be honest.
More greenspot than I’d like to see for sure and my buceps are struggling HARD, I used to keep these with no issue!

Part of me suspects low-light, but at 75 PAR and with these plant varieties, I wouldn’t expect issues. I’m seeing loads of pearling during the mid/late photo period, which leads me to think light is not an issue... tbh, it's so much that it’s almost annoying how many microbubbles there are, lol.

Nitrate/Phosphate seem in range and have been dosing recommended APT3 dose daily, consistently for three weeks now.

Considering:
  • Am I dealing with excess organics as a result of a thick foreground capturing debris (I am getting a lot of debris when I vac/water change
  • Could light be too low?
  • Lesser degree - Could my lighting spectrum choice be impacting plant health?
Our good ‘ol friend, ChatGPT thinks with 80% confidence it’s a biofilm or fungal issue?

Setup:
50g
ADA Amazonia (1/4) & Tropica soil (3/4) substrate (what was on hand)
Oase BioMaster Thermo filter – spray bar right, left intake
Oase Surface skimmer
Yugang CO2 reactor
Fluval Plant 4.0 pro light – 7hrs running ~50% power, except blue at 5% (schedule attached)
Conditioned municipal tapwater – source: Lake Ontario. Note the water does pass through a home water softener (set to lowest setting)
APT 3 dosing – daily dosing as recommended

Parameters (chart timelines attached):
Par reading: 75 μmol/m2/s dry, at substrate depth (measured by Photone iOS app)
Ammonia: 0
Nitrite: 0
Nitrate: 20
pH: 7.2 down to 6.2 with CO2
Phosphate: 1.25ppm
GH: 10
KH: 9
TDS : 250-300
50% water change every 5-7 days, with light substrate vacuum

Stocking:
24 Emerald eye dwarf raspbora
8 Celestial pearl danios
6 Otto cats
6 Amano
Light feeding every 1-2 days

Appreciate folks talking the time to share their thoughts!


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There are many here smarter than me when it comes to water chemistry, but my first thought/question would be; is it wise to use water conditioned with a water softener in an aquarium? Would added sodium cause issues with plant health?
Thanks Jay!
Interesting thought as this is a new house compared to my previous tanks.
Different municipal supply and slightly harder water.

My line of thinking was that given the KH/GH values and that TDS is at reasonable level, with the softener working at very low setting, it wasn't likely a major cause. Though certainly one of the factors to explore further, could be making things worse..

Will test the water pre-softener to compare to post-softener and tank.

Any opinion of what this algae (or other offending stuff) is?
It's not lining up with my understanding or experience with common algae issues.
 
Any opinion of what this algae (or other offending stuff) is?
It's not lining up with my understanding or experience with common algae issues.
Again, I'm no expert, but my first guess would just be diatoms. How long has the tank been up and running?
 
Yeah, part of me wonders the same.

Tank's been up and running since Jan 22.
I went through the common and expected dusty looking diatom phase on some of the rock/plant ~Week 2 of Feb.
While that subsided, since mid March, have had this brown, clumpy, gelatinous stuff continuing to grow very quickly.

I manually remove, change water, couple days later its back with vengeance.

Bike Sunglasses GIF by Xbox
 
We had a water softener in Florida. My plants did a lot better once I started using RO water instead. Usually Oto’s would take care of diatoms pretty quickly, and that tends to go away on its own after the tank matures anyway. Maybe it’s some kind of slime mold?
 
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