Hmm.. ok. good point there mum.

Metricide is, according to google, just the concentrated version of Glutaraldehyde which is sold under various brand names as liquid co2. Bacteria and light help to break it down ultimately to some h2o and some co2. Until it's broken down it acts as an algaecide.

So, what that gets you is some extra co2 in the water, which every green living thing uses when there's light. If you combine that approach with cutting down on the nitrates and phosphates then there's a lot of co2 for the plants to use but no other nutrients. So, no real plant growth.

Approaching this from the other side would be to make sure there's enough trace and macro nutrients so that your plants can use up the co2 and eat up the rest before the algae recover from the metricide attack.

My advise would be to get on a regular dosing regime with the metricide (and regular as in the same amount and as much as possible the same time of day, this stuff is best dosed in the first hour of light) additionally make sure the lights are on a timer and not on too long (10 hrs max, 8 hrs would be good) for human enjoyement you can cut that photo period in 2 so that the lights are on in the morning and in the evening.

Additionally see about getting a phosphate testing kit and test phosphate and nitrates daily during 2 weeks and record that. Combine that with a test of tap water and you can come up with a plan based on what's in the tap and what's in the tank from the fish and fish food.