As with the co2 I was led to believe that it helps keep down the ph level.
I was wondering about this which is why I asked. I don't advise any of these "extras" because of the increased problems. An aquarium has a biological and chemistry balance. This is based upon the source water (the chemistry) and then the fish/invertebrate load (biological). The parameters of the source water are a unit. The pH will be governed by the GH and KH. Other factors like dissolved CO2 also play into it. Natural CO2 is one aspect, and it will affect the pH in relation to the GH and KH. This if left alone will be stable. Water changes will replenish the same parameters. But as soon as you do anything to impact this stability, it opens the door for instability. You are creating another level of balance, but there is always the danger that something will tip the balance. This is why any and all additives are dangerous, aside from the fact that most all of them do detrimentally impact fish health. Keeping things as simple as possible is always more safe for the fish.
We can explore the pH issue if you want, just provide the GH, KH and pH of the source water.
I'm not so sure about the ambient light and window system. I have excellent growth in a tank right under a window. Very little algae, and wonderful reds in the ludwigia. I even have Pistia taking off - a plant I had never before been able to grow indoors. I have very high quality LED plant lights on other tanks, but the plants in that one are thriving. It gets angled direct sunlight, and is surrounded by house plants.
My comment here was solely meant to illustrate how ambient window light can affect the algae. The underlying issue is balance, between the light intensity and duration and the nutrient level. In my situation, over a couple of years I worked this balance out to perfection. None of the eight or nine tanks had problem algae once I got the tank light down to seven hours each day. With eight hours, I had had brush algae issues in some tanks. But once I got the duration down to seven hours, the light intensity and the fish load and the plant load and nutrient supplementation were all in balance. In the winter months with shorter days, this worked fine. But in the summer with the increased daylight, and stronger daylight, coming through west facing windows, it offset the balance and brush algae began to increase. Blocking the light in summer allowed the balance to take control again. For the following five years I had no problem algae.
