Excel would not have been the cause of your brothers algae.
If you are trying to grow carpet plants quickly you need high light to reach them but high light in general means carbon addition since light controls the rate of photosynthesis, high light means faster photosynthesis which means you need more carbon in the water.
Using DIY can be tricky and it will be a lot of hassle at first. Controlling the amount can be difficult and fluctuations in co2
are likely which is not a good thing. A few drops of excel is daily is your best bet but it can have negative effects on some plants.
I actually just asked my brother what happened with his tank and he said that he accidentally got flourish thinking that it was excel then overdosed it. Can you get it at PetSmart? He said it kills algae? I'm just confused on why I can't get this plant to grow because everyone says it's extremely easy to grow and can even be a hassle because it grows too fast for some setups.