Help Photo period for a tank in a room with a lot of indirect light?

[Fishstery]

Hey all! Please excuse any weird formatting, I'm new to the site and this is my first post, so I'm still learning the ins and outs with the site.

I'm finally getting back into the high-tech side of the hobby after a few year hiatus as I tackled my new title of "mom". Now that my kiddo is a (somewhat) less demanding toddler, I'm ready to take on another high-tech setup.

While I am well versed enough after having high-tech setups prior, I always kept nano tanks. My newest project is far larger than any tank I've kept to date. Some relevant details:
Landen 100p ~52 gallons (probably around 45 filled counting water displacement)
Garden style hybrid
UNS controsoil
Oase Biomaster 600
5lb co2 tank with dual-stage regulator and inline diffuser placed as close to the canister as possible on the outflow line
Two Week Aqua T90 Pro lights

I'm going to be setting the lights up, planting, and dialing in co2 on Friday and Saturday, but I'm running into a conundrum with my lighting schedule that I'm hoping some more experienced people can give input on. The tank is in my open concept living room, with two walls of tall windows. The tank is situated against the only wall without windows, and there is at least a 6 foot radius from the nearest window. There won't be any direct sunlight hitting the tank thanks to our tree line in the back, but the room gets a ton of natural, indirect light.

I like to set my lights to come on later in the afternoon, so that by the time I get home at 5pm and get my son to bed at 8pm, I'm still able to enjoy and observe the tanks. I hate flipping the lights back on after they've been off for a few hours, just so I can check in on my fish and enjoy the tank, mostly because it disturbs the tank inhabitants. My kiddo is also an in-training aquarium enthusiast, to my delight, so he likes to be able to watch them when we get home as well.

I'm concerned about this tank however, because the sun is up around 8am, so the indirect light will fill up the room early in the morning. I plan on having a longer ramp-up time for co2 before the photo period begins, so around 3 hours to start (obviously subject to change as I dial-in). I'm also going to be renting a PAR meter from my LFS to get the umols for all the different light and height settings on the Week Aquas, so that I can have that data to dial in lighting as needed.

With all of this to consider, am I SOL on having a late day photoperiod? Will the indirect sunlight cause issues with co2 consumption if I try to have the lights come on many hours after the plants have access to that indirect light? What suggestions do you all have as to go about this, and suggested photoperiod start and end time? "Sunrise/Sunset" Ramps, or no? Suggested PAR at the substrate?

I'm growing some moderately demanding plants, a few heavy feeders like Cabomba Furcata and Nymphaea sp. Peru Puerto Maldonado. Some that appreciate higher light such as Rotala Macandra species, mini included, as well as Rotala Floridia. My main concern is algae, I battled it a lot in my first dutch hybrid tank due to inexperience and it really put a damper on my ability to enjoy it. Any help is appreciated

 

[Koan]

Similar question actually just came up last week

Post in thread 'Lighting Questions'

Jan 11, 2026

Does getting the indirect sunlight mess with the plants photo period or does it not really matter?

It might, it might not! But it's definitely one variable that can mess a tank up. Removing direct sunlight can be really helpful. Most professional galleries do not allow a single bit of sunlight to hit their tanks.

You can use the Photone app on your phone, with either a DIY paper diffuser or the cosine diffuser accessory, to get an accurate measurement of the amount of PAR hitting your aquarium from the sunlight.

Here's my tank in the winter. The low Colorado sun hits...

• Naturescapes_Rocco

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[Fishstery]

Similar question actually just came up last week

Post in thread 'Lighting Questions'

Jan 11, 2026

Does getting the indirect sunlight mess with the plants photo period or does it not really matter?

It might, it might not! But it's definitely one variable that can mess a tank up. Removing direct sunlight can be really helpful. Most professional galleries do not allow a single bit of sunlight to hit their tanks.

You can use the Photone app on your phone, with either a DIY paper diffuser or the cosine diffuser accessory, to get an accurate measurement of the amount of PAR hitting your aquarium from the sunlight.

Here's my tank in the winter. The low Colorado sun hits...

• Naturescapes_Rocco

• 
• 
• 

Yes I did read that thread prior to posting, actually! But it didn't address my main question, on if it is then necessary to start the photoperiod at the same time the indirect sunlight begins, or no harm no foul for the tank to get those few hours of indirect light, then ramp up co2 and begin the true photoperiod later.

Also in the case with Rocco, that was in regards to direct light. I'm fortunate enough that there will be no indirect light, and due to the tree lines on all sides of the house, even the indirect light isn't very bright unless it's a sunny summer day. I did takeaway his tip for using a PAR meter app to at least get some kind of general understanding of the light coming in. I can also take a reading with the real PAR meter in the tank with the Week Aquas off but indirect light coming in, to get a better understanding of the actual light intensity. Perhaps it would be easier to answer my question once I'm able to put an actual data value on that.

I'm taking a vacation day from work tomorrow and Friday to tinker with the setup and recieve my fish and plant orders, I will update this thread with what I find with the PAR meter, and a picture of the tank's positioning in the room for others to reference to in the future, should this topic come up again.

Hopefully in the meantime this thread gets a little more traction and others can chime in on their thoughts as well! Thank you for the reply!

 

[Kwyet]

I’m not an expert, but I think if you have a lot of indirect light then the plants will be photosynthesizing, and it would be best to have your CO2 going at least a couple of hours before that.

 

[techman81]

I wasn't sure of the word I was looking for so had to look it up. Nyctinasty: The circadian rhythmic movement of plants, often called "sleeping movements," where leaves or flowers close at night and open during the day in response to darkness or light changes, controlled by an internal biological clock

Why do I mention that? Because observations of this phenomena in my own aquarium plants and the relatively low amount of morning indirect light I have in my house, leads me to believe that the plants are ready to go as soon as they sense that change. So I would agree with @Kwyet, photosynthesis is starting as soon as the plants wake up, regardless of if the tank light is on or how bright the indirect light is. In my case, I still don't have the photoperiod start until around 11:00-11:30 am though and then there is a 30 minute ramp-up. I start my CO2 3-4 hours before that.

Now, one of our many biology/botanist folks can chime in.