substrate heating and lighting

["Roxanne Bittman" <rbittman at dfg_ca.gov>]

>>>Question 1 (Substrate heating):
From reading many articles in various sites, substrate heating is 
recommended by many people for long term growth and maintenance of a
planted 
aquaria. 
a) Wouldn't this mean that the biochemical processes and water
'movement' in 
the substrate be limited to times where the plants are not
photosynthesing?>>>

Yes, it does mean that.  Many of my North American aquarist friends do
not use heat cables because they are off most of the summer.  Their
benefit is a little hard to prove too and some of us don't believe they
are worth the expense and trouble.  I would either heat with traditional
heaters or use an under-tank reptile plastic strip heater, which is what
I use myself.  They are very inexpensive.   It does not provide the
substrate mixing but it provides "warm feet" for the plants, which some
plants like.  I still turn it off in summer.

Question 2 (Lighting):
>>>The generally accepted figure for a normal planted tank is 2-4watts

(depending on plant selection, aquarium depth etc). This figure seems
to be 
only pertinent to fl?
a) What are the generally accepted figure for those using metal
halides? Do 
I have enough? I am planning to keep a mixture of fast (e.g. hygros)
and 
slower growing plants (e.g. anubias sp. Java ferns) in various regions
of 
the tank.>>>

With even some high light plants, you will need more than 2 watts/gal
to get good growth.  I don't know the calculation for halides, but I'm
sure it's not like that for fluorescents.  I believe the 2-4watts/gal
only apply to standard fluorescents.  Those of us using power compact
fluorescent lights certainly often brighten our tanks with more than 4
watts/gal.  Hopefully, someone who has used metal halides can answer the
"is it enough?" part of the question.

Roxanne Bittman