Myriophyllum mattogrossense, white tips. Possibly intense lighting? Low nitrate?

The tips of my Myriophyllum mattogrossense have gotten white, is this a sign of low nitrate? or perhaps intense lighting? I am very high tech, here is what I have running...

60 Gallon acrylic heavily planted tank
Pressurized co2, Co2 is diffused via eheim's 2217 outtake through glass inline co2 diffuser (Co2 goes on when lights go on) very effective diffusion method, co2 mist streams everywhere.
4 WPG (On 7 hours)
NPK (esti. index), trace
50% W/C every week

I follow this plant food regime...

40-60 Gallons
1/2 tsp KNO3 3x a week
1/8 tsp KH2PO4 3x a week
1/8 tsp K2SO4 3x a week
1/8 tsp (10 ml) traces 3x a week

I have been dosing 1/8 tsp. of KNO3 recently, when I should really dose a little more than that, like 1/2 tsp, however, I know my fish load is high enough so I thought why bother adding more KNO3? My nitrate is usually at 10 ppm after the end of the week before I water change. Well, here is my stock,

60 gallons. Had the rainbows for about a year, and they are getting bigger.

5 Boosemani rainbows (not fully grown to 5 in)
1 Turquiose rainbow (not fully grown to 4 in)
2 Congo tetras (Fully grown)
2 Red line torpedo barbs (Not fully grown to 6")
5 Sterbai corydoras (Not fully grown to 2 and a half in)
10 Rummynose tetras (Fully grown)
10 Cardinal tetras (Fully grown)
3 Golden white minnows

Filters:
Eheim 2217
Fluval 305

Should I add a little more KNO3? 3 WPG instead of 4? Get the high light out of plant's way? Let it be somewhat shaded?