Brown algae

[Bobo8]

I take care of some tanks for this business. This one tank a 75 gallon, is getting really bad brown algae build up! I don't know what is causing is.
I do a 30 ish gallon water change every week or at least every 2 weeks. There are 2 filters running. A Rena Filstar xp3 I believe and a fluval 406.
Water parameters are as good as they will get as they do not allow any chemicals to be used. I do use clearmax and carbon in the filters. Which one filter is changed per month.
There are only 6 small angelfish in this tank. Overfeeding is not a factor as far as I'm aware.
There was a piece of driftwood in here which I removed .. wondering if that could have been the cause.
Anyway here are some pics if someone could provide some insight!!

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[Bobo8]

Other filter

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[RackinRocky]

I'm confused. You say water parameters are as good as they're going to get without using chemicals? And you are using stick testers? These are NOT accurate. You need an API test kit that includes PH, ammonia, nitrites and Nitrates. You shouldn't have to use chemicals at all if tank has been properly cycled prior to adding fish. I have brown algae on a cave and tiki hut in one of my tanks, and it makes things look natural, so I just leave it. Sounds as if you need a bit of research on how to care for tanks properly. Get rid of the test sticks!

 

[Bobo8]

Haha oh don't worry I have the master API test kit. That's just what they buy me to use. They told me I didn't even need to test the water hahah. Pretty sure I know what I'm doing just thought I'd see if anyone knew. Thanks for making me feel stupid! ?

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[Bobo8]

They pretty much don't do anything I say so I have to make due with what I have.

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[Caliban07]

Not sure about the cause of this one. Excess light, bacterial imbalance? It usually subsides on its own. Ottos and nerite snails would be a good shout to get rid of it.

As for preventing it. Reduce light, change more water, clean filters more regularly etc.


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[Magnum 350]

That looks like diatoms. Not an algae but a single cell animal. They need silicate to thrive. Test the water for this. If the water you are using is high in silicate they will eventually encrust everything. As for light diatoms can grow with almost none.