I have several echinodorus, in my 600 liters tank (about 130 galons i
believe).
It's 160 gallons U.S. Not many people use U.K. gallons any more, since they've
converted to metric and use liters now.
Could the yellow leaves be because of some nutrient dificiency.
Possibly. It could also just be old leaves. Echinodorus leaves don't last
forever. Prune the old ones off when they start looking ratty. New ones will
replace them quickly enough.
I have also
very few watt per gallon (i have the total of 116 Watts with 2 x 58 Watts
Bulbs).
That is less than a watt per gallon. But given the size of your tank, it is
probably enough. If lighting were a problem, I'd expect your anubias to be
doing well while your other plants suffered.
My PH is very high (about 7,6 to 7,8) even doing DIY CO2. But i donīt think
that this as anything to do with my problem.
Egad. I doubt DIY CO2 would be adequate for a 160 gallon tank. Do you know
what your KH is? How about your nitrate levels?
You might find this page useful:
http://www.csd.net/~cgadd/aqua/art_plant_nutrient.htm
Also..what kind of fish are in your tank, besides loaches? Do you have any
plecos? They sometimes scrape flat leaves too close, leaving yellow spots and
even holes. You can recognize pleco damage by the "frayed" look.
Leigh
http://www.fortunecity.com/lavender/halloween/881/