Brown Diatom Problem

[WhoIsRoscoe]

I'm really hoping to get some advice on a persistent brown algae problem in my tank. I believe it's diatoms, but I'm honestly not sure what's causing it or why it keeps coming back.

I'm a dad with two kids under two, so my free time is limited. I love this hobby, but it's becoming frustrating when no matter how much effort I put into maintaining my tank, this brown gunk returns week after week.

My setup:

• Tank: 125-gallon, heavily planted, running since May 2026
• Substrate: Fluval Stratum aquasoil
• Filtration: Two Fluval FX6 canister filters
• Water changes: 50% every Saturday
• CO₂: Injected and stable
• Fertilization: Joe Harvey Macro/Micro, following recommended dosing
• Lighting: Two Week Aqua 900L fixtures, 7-hour photoperiod at relatively moderate intensity

I'll attach photos of my tank and lighting settings.

For transparency, the photos show 10 days without a water change, which isn't typical for me. However, even after 7 days, the amount of brown buildup seems excessive.

I understand diatoms are common in newer tanks, but mine has been running for nearly six months. I'm really trying to identify the root cause rather than continuously cleaning up the symptoms.

At this point, I'm spending more time fighting algae than enjoying the tank, and with my limited free time, I really need to find a sustainable solution.

Has anyone experienced something similar or have suggestions on what I should investigate?

I genuinely appreciate anyone taking the time to help. Thank you!

 

[FreshTides_Neal]

Are you using tap water? Diatom algae has been popping up in a few tanks at my store recently. I haven't bothered to test but my guess would be more silicates in the water supply causing it in my case. It couldn't hurt to test your source water.