You need to be dosing nitrates, phosphates, potassium and traces, in addition to carbon (Excel). Then, cut back on the light duration to about 8 hours a day. I suggest you forget about testing for the nutrients, and at least for now, just use the EI method of dosing - see http://www.aquaticplantcentral.com/...al.com/forumapc/science-of-fertilizing/15225-estimative-index-dosing-guide.html. You will need to physically remove or kill the algae that is now in the tank in order to get rid of it and reduce the chances of it spreading.

 

Er? Pictures would be helpful.

Is it growing around the individual pieces of your substrate, or is it growing directly on it?

If it grows around the substrate and has the consistency of a tough brillo pad, then you, my friend, have a case of cladophora.

 

Having looked at the photos available of this clado stuff and compared them with what is in my tank I think this could well be it. Would I be right in thinking that removal by hand of what I can and a strong dose of seachem execl would at least reduce the problem?

 

1) Remove all you can by hand, prune plants that have it tangled in, ie: java moss, hairgrass, etc...
2) Dose Excel per the directions for the INITIAL dose.
3) Overdose Excel (2x - 3x) for the later doses.
---When you're doing over Excel OD, you can spot treat affected areas but not that it'll probably kill off any riccia, fissidens, anacharis, vals, and possibly HC.
4) Get Amano shrimp, they seem to eat away at any smaller bits of cladophora left.
5) Constantly remove any bits you see manually.