Algae growth at 1 wpg

You should go non-CO2 if that is your goal and not no dosing while still with CO2 enrichment. Plants grow 10-20x faster with CO2 enrichment and no dosing means limitation and thus poor growth. Plants that are not growing makes excellent substrate for algae.

Regards,
Peter Gwee

 

I'm guessing that you have green dust algae, from your description. You can get rid of that, but it is hard work. I suggest that you start by allowing it to grow unmolested until it turns brownish, starts to fall off the glass in splotches, and is clearly at the end of its life cycle. Then work hard to remove all of it from the glass, and hardscape, and, as much as possible from the plants. Change about 75% of the water to get rid of the debris from the algae. Next day, do the same thing. Next day do the same thing again. Keep the filter as clean as you can during this time. Dose Excel as a further aid against the algae. Then see if it comes back.

If it comes back, it should be much less dense than before. But, repeat the above again. It might even take going through that three times before it doesn't come back again.

 

Plants needs fertilizers (food) and it has to come from somewhere be it the substrate or water column. If you supply enough via the substrate, then it is fine. I cannot account for what you are using for the substrate thus I will advice you to add some to rule it out. Remember that plants still need food and not dosing doesn't mean it didn't need fertilizer but rather it came from some other source.

For the algae, you need to go in and remove them and then correct conditions necessary for good plant growth. Not sure about the light but it might be too intense at one particular spot even at 1wpg. You would need a better spread of lower wattage light vs 1wpg of high light bulb. (eg. 2x20w NO FL over a 20gal vs a 55w PL).

Regards,
Peter Gwee

 

I'm not sure if this will apply to your situation, but I had a terrible outbreak of algae one time and the only thing that cured it in the end was the complete removal of the substrate (which I didn't do to fix the algae problem...but it fixed it). I had been lax about gravel vacuuming and it led to a huge buildup of organic nutrients in the substrate which was just feeding the algae. Once I did that, and started dosing ferts, things settled down into a much better pattern and I was able to cut back and virtually eliminate dosing after it got straightened out. Getting it straightened out once it goes wrong is the hard part and eliminating organic nutrients by gravel vacuuming a lot and then dosing inorganic nutrients may be what you need to do to get the algae situation under control. Personally I would continue with diy co2 if you can keep it stable, until the algae situation gets better. Removing it will probably make things temporarily worse as the plants readapt to non-co2, and it's better to make things worse when they are semi-under control than to take a bad situation and get it even more out of control, if that makes sense.

Also if you have bba, in my recent experiences with it the only thing that kills it is bleach. A 1:20 ratio and soak the plant for 3 - 5 minutes, then rinse well. This may kill the plant but it works as a last resort for plants you don't want to have to throw out. I would imagine this will kill most types of algae.