Why algae without co2? Why would this cause it?
basic photosynthesis here at play. There are 3 things we need to assure in a planted tank. Light, Nutrients and CO2
Too much light causes plants to want to grow real fast. This means plants will use up all nutrients and CO2 quicker. Once exhausted plants can not grow and will show deficiencies and this excess light feeds algae growth on your now weak dying plants.
Too little light, and/or not enough CO2 means the plants won't grow well and will start to melt and rot and algae will start to win
Basically the thought today is to ensure your light can be moved up and down and/or dimmed. Moving it further away reduces intensity and of course closer increases. Dimming also works. Having this dynamic in your lighting is most important.
Finding the right balance of light that promotes plant growth and doesn't cause algae is something you have to discover. The amount of nutrients needed corresponds to the amount of light and CO2 present. If light and Co2 are present then the plants will use any nutrients they have available to grow. Here we figure out enough nutrients to ensure growth and no deficiencies. Excess nutrients (to a reasonable expectation) are OK if the proper amount of Light and enough CO2 are present.
If you are not going to use CO2 injection and you are going with medium light you shouldl research Liquid CO2. Its not as good as Co2 gas injection but it is useful to add. I have Co2 injection and I use liquid CO2.
However you MUST UNDERSTAND WITH ALL THESE ADDED NUTRIENTS CO2 ETC.. THAT YOU MUST CHANGE YOUR WATER 50% ONCE EVERY WEEK OR 2 AT MOST. You also must trim regularly. Over growth shads bottom leafs and smaller plants. Older leafs will melt away and will need to be removed occasionally
Also WATER FLOW. You must ensure that water is flowing to all the corners of your tank. you want to ensure nutrients/CO2 are circulating everywhere your plants are. Dead spots happen because of flow issues