Brownish stuff on leaves

[Liquid-]

I have had my tank running for about 14days now.
25gallon with DIY co2, 75watts and fert (Sera Florena) acording to the bottle.

light on: 10hours
Ph: 6.8 (average)
kh: 4
NO2: 0
NO3: 0
PO4: ?

Plants so far:

4 : Labelia cardinalis (splitted to about 7 single stems)
4 : Cryptocoryne x willisii (splitted to about 8 single plants)
2 : Cladophora aegagropila
1 : Anubias barteri var. nana
and about 5-6 stems of Ceratophyllum demersum (hornwort).

And fish:

4 red neon
and
2 Papiliochromis ramirezi

All plants shows nice growth, especially the Ceratophyllum demersum.
But there are now showing some brown patches on all plant leaves except the Ceratophyllum demersum.
I guess it must be algae, and i have seen it before in some of my breeding tanks, were i just let it grow, and it soon developed into very long brown hair algae all over the tank. This doesnt matter in my breeding tanks. But i am now scared that the same thing will happen in my new display tank...

So far i have just removed it from the leaves by gently rubbing 'em with my fingers, but i really would like to kill the problem for good.

Any good ideas...i know my information is poor, and my english isnt A+

ps. I have a picture of my tank, but dont have a place to upload yet.

[PeterGwee]

CO2 and nutrient issue (N,P,K and traces). At 3wpg, you are driving the tank fast and bad things happen fast as well. Consider lowering the light to 1.5-2wpg to have more wiggle room. Dose nutrients (you only have traces for the moment and are not dosing any macros which is a problem.), do weekly large water changes and keep up on the CO2 (6.5-6.6 for your KH of 4..its going to be alot of work for DIY).

Regards
Peter Gwee

[Liquid-]

Thnx...I have tried shutting off one of the lights, and starting to change more water (about 30% once a week)...

But i have a question, it may be stupid for some of you, but we are all beginners..

I guess traces are Trace elements, like fx iron (am i wrong?)
...but what are macros?

Thnx again, and just want to say that it is really nice to find a dedicated planted tank forum (hard to find a serious one in this part of europe

Best Regards
Jonah

[PeterGwee]

Macros..Nitrate, phosphate, potassium, calcium and magnesium.

Since you live europe, you might want to get a report from your local water authority on the tap water parameters.

Regards
Peter Gwee