Hi all,
Dave, I have just looked back through this post, I think what you need is some
stability. Because of this I would recommend taking off the worst effected leaves, but leaving everything else the same for a couple of months. At that point you can review your fish health, plant growth and algae and decide what you want to do.
At the risk of sounding terribly monotonous.lol. Increase the use of your ferts (micros + macros) and increase the CO2.
This does work, you only need to look at Phoenix44's posts for definitive proof, but I'm convinced it is a method which increases the possibilities of things going wrong, and then you end up changing this, lowering that etc without really knowing where you are starting from.
CO2
As you ramp your CO2 up you increase the risk of stressing your fish through sub-lethal CO2 poisoning, this is due to the "Bohr Effect", where the higher CO2 levels lead to less full oxygenation of the blood. If you do raise your CO2 you need to make sure the water is fully oxygenated and your biological filtration running at its optimum capacity. During the day this is not a problem as enhanced CO2 will increase photosynthesis and O2 production, but when the plants aren't photosynthesising you need to drive off the excess CO2 as rapidly as possible (so probably run an air pump at night). The other problem with CO2 is that if you have a CO2 dump into the tank at the end of a cylinder etc. it will kill your fish.
Personally whatever the advantages are of CO2 for plant growth I won't use it because of the toxicity issues.
You also need to remember that your floating plants have the "aerial advantage", access to atmospheric CO2, and this means that levels of CO2 in the water are irrelevant to them.
Fertiliser
Again as you increase the levels of your ferts, (micros + macros), you definitely enhance plant growth (as long as CO2 or light aren't limiting), but you are adding more salts and nutrients to the water and this raises the potential for things to get out of balance, potentially leading to other algal and water quality problems.
I think of this like juggling, the more variables you add into the system, the more balls you have to juggle and the higher the level of light, CO2 and nutrients the higher those balls are thrown into the air.
Because of my lack of juggling ability I like to concentrate on retaining low levels of nutrients (using the "Duckweed index"), so that plant growth is nutrient limited. You can think of this as a low juggle with as fewer balls as possible.
The advantage of this "KISS (keep it simple stupid) approach" is that changes happen slowly and it gives you stability. The disadvantages are that the range of plants you can grow is limited, and because of the slow turn over of leaves, you always have some algae on the older leaves, usually BBA, Stags horn and a fine fuzz of green algae.
But I'd much rather have stability and algae, and that is my choice.
cheers Darrel