Fertilizers

So I have a 55 gallon 108w T5HO planted tank.

Plant list:
amazonian swords (2)
melon sword
water wisteria (4 stalks)
ludwigia (6 stalks)
java fern
anubia wrinkle leaf
and next week dwarf hair grass which I hope to carpet the bottom of my tank

I ran out of an Iron supplement I was using. Originally I bought it because I was having an iron deficiency in my previous ten gallon when I had it running. Once I switched to flourish and the 55 gallon I kept using it just to use it.

My question is do I need to use an iron supplement? I use flourish and excel. I'm not trying to get an award winning planted aquarium but I do want the plants to keep their nice colors. My ludwigia's have a very nice blood red after I dose the tank. Wondering if this will keep happening without dosing iron? I also saw that you can buy potassium and nitrogen from seachem. Wondering if I need this at all? Thanks for the help. BTW my tank has been running for 6 months like this. =P

I'm not sure if the ludwigia would benefit from dry ferts though. They have very shallow roots. I'm also using eco complete so I originally thought I wouldn't need iron. Thing is, I only dose once a week because that is what my plants need. But around the end of the week my ludwigia lose the red color. I just never have not used iron supplement to see if it would be enough with just plain flourish.

Didn't know that part

So then I should use flourish and excel regularly with the tabs being replaced every 3 months? Sounds more economical than buying seachem iron.

Oh I thought he meant tabs >.> hmm dunno about dry ferts.

Is potassium really a must? I haven't seen any signs that show that I need it. But when I do add the dwarf hairgrass I expect it to suck up a lot of nutrients once it carpets.