High nutrient loads. Lots of phosphates and nitrogen. Cleaning and big water changes are very short term. Either stop loading up the aquarium with too many fish that need food..or plant heavy,dose iron, to out compete the algae. The iron unlocks the plants ability to take up those nutrients.
You could lower the lighting...but that's not going improve the plants..just finish them off.
No problem..just remember you have to change conditions. Water changes (least problems),Peroxide(danger!),antibiotics (costly but will work)can eliminate algae...with side effects,let me tell you,so best to get a better or larger filter,more plants,and dose the iron..
Your playing with fire with Peroxide. Plus,what it does to higher plants takes longer to show. Not going to quibble over nitrogen yes or no,but all in one land ferts( miracle grow) with it..and the others,caused instant blue green algae for me. Not huge since my tank is established,and water changes plus stopping the use of land ferts for now,put it back in remission.
Blue green algae is a nutrient overload and warm water creation. Why local recreational ponds get it here in summer and not the rest of the year. Its also toxic to fish. I've had fish die actually ingesting small amounts of it foraging in the aquarium. Loaches especially but catfish and others too.
I've used it decently a few times and I is not so dangerous. Though, I have fish-less tanks mainly. It has effect on higher plants for sure, I noticed myself that maybe cause of peroxide usage or sth else it took them some time to recover and start growing again. They don't rot. But I fight with BGA for some time and was really pleased it can be reduced this way quite cheaply and easily, tank is perfectly clean and you got a new chance. But it's necessary to change the cause.
Panda Garra will eat BBA. They will eat hair algae that is STARTING..maybe not when it's long and tough. I've had them mow down cladophora algae also.
The aquarium that has them and Ancistrus and other helpers makes for a healthier aquarium.
Never found a thing that eats BGA. Must be something...but it might turn out that something is small and you could never get the fish to not eat IT.
I had BGA forming on some crypt parva in one of my new tanks. I was just about to treat it when i realized my Oto's were eating it. I left it alone and within 48 hours the Parva was picked clean and it hasn't come back in over 10 days.
Somebody told me that the Siamese Algae Eater takes on BGA. I can't vouch for them.
Really,they are caused by too much nutrients no.1, unhealthy plants not taking in that nutrients due to the wrong lighting or lack of iron, and a tank with low oxygen are the perfect storm of it.
Clean the tank well,change lots of water and make sure you have the right amount of filter media..to break things down faster. Keep temps no warmer than 75f helps too.