I Really Must Be Losing It!!

Hi,
Please find attached a rough guide to my tank and pumps/flow.

Tank has about 160 Litres in it.

I must be doing something wrong. I am injecting 4 bubbles per second.

I was starting my CO2 2hrs before lights on. When the lights go on the drop checker is showing blue..not a dark blue, but blue all the same, after the 2 hours of CO2.

Now, I thought that when the lights come on, the water would be fully loaded with CO2, but no. Then 2 hours after the lights come, on the drop checker reaches green, and then by about 2 hrs before lights off the drop checker reaches a lime green.

Today I thought I would try something different. I had the CO2 come on 2 3/4 hours before lights on and.......... the drop checker was still blue. I have just checked my drop checker ( 3/4hr after lights on) and it is turning green so there is an improvement but I am still unsure what is happening.

Having the CO2 switched on for 3 1/2hrs until  I see a change seems a bit excessive. It means I have 9 3/4 hrs of CO2 for 8 hrs of light.

As far as I can see I have very good flow everywhere with all plants showing  movement. I don't see pearling either.

I also have algae returning. When I do a bit of research I just keep getting differing opinions and answers.

One of my main niggles is that I keep reading that lack of or fluctuating CO2 is the main cause of algae problems.

I cannot increase the CO2 any more as the fish will hang near the surface. I have an Eheim Pro 3 at 950 lph, one small submersible at 200 lph and a New Wave circulation pump running at 1600 lph and I have a good flow using these. So am now at a loss as to what to do.