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900 Watt Mars II -Too Much?


Active Member
Hello all, I was prepared to start the journal for my first grow today, but after just a few hours into 12/12 under my Mars II 900, my Blueberry is looking pretty unhappy:

The reason I believe it's the light is that I've tried to use it with my plants before, and every time they have gotten wilty after a few hours under it. I put them back under my 250 watt (actual) CFl and they perk right up. I've tried this several times before with enough other variables to make me lean toward the light as being the culprit. I bought the light through an auction on Mars Hydro's eBay store and I got a smoking deal on it (I paid less than what the 700 watt model sells for), but it is definitely more light than I had planned on buying. Here are the details:

Strain: DJ Short Blueberry, vegged from seed since 9/27 under the aforementioned CFL.
Setup: 5-gallon DWC, medium Active Aqua stone with GH dual diaphragm pump. I have had some res temp issues in the past which have since been [mostly] corrected.
Nutes: JR Peters Jack's Hydro 5-12-26 @ 3g/gal, Calnit @ 2g/gal, Epsom @ 1g/gal. All in plain ole tap water, which my TDS meter reads as 87 ppm. I use three mils of 35% H2O3 and 3/4 tsp Dutch Master Gold Zone per res change.

I have been setting the pH between 5.2 and 5.8 during weekly res changes and topping off with pH water as needed. I've been pretty good with checking it most days to make sure nothing has gone horribly awry, which thankfully has not happened yet. I let the pH swing a little on its own but have been adding pH down the few times it climbed toward the top end of the cannabis comfort zone.

The top of the canopy is ~2' from the light. The light is as high as it can go in my cabinet. Temps climb a little when this light is on but still remain in the low 80s. My humidity will always be low due to my climate and I have been holding out on buying a humidifier because I'd like to keep this thing as simple as I can. In any case, I'm pretty sure that humidity is not the issue here. The whole contraption is ventilated into the attic by a 6" Ventech inline fan and carbon filter that I bought off Amazon.

What should I do? According to the Mars website, flower should be 12-18" above the canopy and veg 18"-24", which this certainly is, but my area is just shy of 2' by 4' and is smaller than the claimed footprint of 4' by 4' for the light. I can rig up a bank of 2700k twirly CFLs that will get me through this, but I'd like to use my Mars II since that's what I have. Is this something the plant will snap out of if I give it a day or two? I've done all the research about light stress I could, but the example pictures I could find didn't match symptoms found on my plant, not to mention a lot of people don't even think too much light is even possible.

Here's the whole setup, which I have built into my closet. If anyone sees any other issues/fire hazards/possible sources for cold fusion/spectral images feel free to comment:

Grow journal to follow soon, hopefully.

Thanks for stopping by!:thanks:


On Vacation
Here are my 2 cents.

I think the low humidity and that light are the problem, the easiest way to find out is to add humidity and see if it resolves the issue. If you don't want to buy a humidifier then leave a shallow pan in front of the fan and fill it with water, refill often to keep humidity up.

Green Dreamz

New Member
Re: 900 Watt Mars II--Too Much?

Hey iluvsnow.....i am not an expert but i believe the range for your ph should be 5.5 to 6.2 for hydro.....i run mine at 5.8......also i run a 700watt mars and i normally keep the light with 18 inches and as close as 12 but there are members here that aree much closer than that with no issues......maybe the light intensity difference from cfl is too much at first but i would keep using it for the next couple of days and just monitor that she doesnt get worse......as far as humidity goes there is a member here...and for the life of me my high ass cant remember who, but they hang a wet towel with a clothes hanger i believe with great results on raising the humidity....i think that he changes it a couple times a day, but a cheap and effective way.....other than that buddy i say keep trucking .....i think she is just in shock with the difference in useable light that from that 900:)......like i said i am no expert by no means but if theres anything i can do to help out just let me know:):):Namaste:


420 Sponsor
Re: 900 Watt Mars II--Too Much?

Hello iluvsnow, your light is too big for one small plants, you'd better hang higher, you need to do some adjust yourself according to the plants grow.


Active Member


New Member
Can you turn off part of the light for a few days. It will recover but it may take a few days to adjust to the intense LED.


Active Member
I have the Mars 900 watt in a 4x4 tent scrog with one 00 Kush plant and in veg I needed to keep the light 27"or 28" above plant and during flower let it grow into the light down to 22" above plant then after a couple weeks I moved it down to 18" above the plant and that is as close as it likes, now on day 61 of flower. during veg I would move the light closer but after a few hours it did,nt like it that close,the Kush grows well under the mars 900 watt.;)

Dave Groomer

Well-Known Member
I think most of the advise here is sound. IMHO the problem is that it is too much all at once for your plant. When switching from CFL to LED they need to to it gradually. I am not sure if you have the space, but if you could raise your light to 30-36" about the canopy then move it down a couple inches every 2 or 3 days you should be able to get her used to it. 18" is about where I have my 900 above my plants. :peace:
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