How Long Should My Photoperiod Be?

[Robbo89]

Just wondering how many hours of light per day I should be giving my planted tank?
 
Light is currently on from 2pm - 8pm so 6 hours a day, at 1WPG (20W, 20 gal). 
 
Specie's list:
 
Hygrophila balsamica? (back left) - 3 weeks since added, growing well.
 
Cryptocoryne wendtii (around coconut) - 3 weeks since added, starting to melt.
 
Vallisneria tortifolia / Corkscrew Val (back right) - 3 days since added, doing alright. 
 
 

 
 
It should also be noted that there are 4 platys in there, which like to scour the tank for algae.
 
Cheers.

 

 

[snazy]

6 hrs is fine for a start until the plants fill in a bit more then you can slowly increase.. 8 hrs is best in a low tech in my opinion, not too long to get algae and not too short for your plants to almost stop growing.
 
It's strange that the crypt is melting after 3 weeks. This indicates CO2 levels have decreased. You may need to check if they get enough flow where they are.

 

[Robbo89]

6 hrs is fine for a start until the plants fill in a bit more then you can slowly increase.. 8 hrs is best in a low tech in my opinion, not too long to get algae and not too short for your plants to almost stop growing.
 
It's strange that the crypt is melting after 3 weeks. This indicates CO2 levels have decreased. You may need to check if they get enough flow where they are.

 
From what I can tell all the crypt leaves, including those that are melting, are 'swaying' in the water from the flow
 
Also, the external filter intake pipe sits in that far back right corner, so it is pretty much surrounded by the crypts, meaning water must be passing over them to get to out of the tank  
 
Not al the leaves are melting, probably about 20-30%. 
 
After how long should I start to increase the light period? like 1 extra hour a week until up to 8 hours?

 

[snazy]

I'd say it's too early. You need good and steady growth. Maybe wait for that crypt to recover and some of the rest to fill in which may take a few weeks.
Once you increase by 30min-1hr, leave it like that for a couple of weeks at least, to see if the plants grow well and watch out for signs of algae. The tank maybe ok with 6hrs, 7hrs or 8hrs, but you really need to give it time each time to make sure the plants aren't suffereing and algae doesn't grow, because by boosting the light, you are causing more demand for CO2 and nutritients and if the ratio between bioload/food and naturally produced nutritients and co2 by the tank can't provide for that rate of growth demanded by the light, then you need to dial back as early as possible before you end up with an algae infested tank.
 
And also, if the crypt is melting, and is getting enough flow, it's maybe wise you decrease the light even further for the time being. It's better if you decrease the intensity temporarily. Can you remove a reflector or block some light somehow? It's still CO2 related, otherwise that crypt would have melted 3 weeks ago, not now.