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Discussion Starter · #1 ·
I have a 90 gallon 48"L 18"W 24"H with a 4 bulb t5 fixture about 8" from the surface of the water. I run two 6500k bulbs that came with the fixture (grow light fixture), 1 KZ Fiji Purple, and one Giesemann super flora.

Is this enough light to be considered high light, enough to grow dwarf hairgrass? It doesn't seem bright enough and I'm starting to think I should have went with a 6 bulb.

Anyone have experience with a 4 bulb t5 on a 90 gallon?
 

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I surprised you got no response. I have a four bulb over my 19" wide tank and it was enough light to grow anything, but I did end up adding a single T5 fixture in back just to make sure I had full coverage. The six bulb fixture was just a little too wide.

I would replace the bulbs that came with it, as fhey are usually junk, are you sure theyre not just standard T5s? Regardless, I would replace those two bulbs, try adding another Flora bulb and a Geismann Tropic is my suggestion.
 

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I saw your post but forgot to reply. I used 4 bulbs over my 90 gallon 48x24x18 so a bit shallower but the light fixture is 10" above the rim of the tank and It will grow anything just fine.

Now to be clear I have an 8 bulb fixture but only used 4 at a time back then. I found the stems in the back corners appreciated the outer most bulbs above them for half the photo period. Since your tank is only 18" this won't be a big issue. Here are a couple pictures to illustrate the 4 bulb at a time setup I used. Pics are of different bulb combos that I didn't run together but gives you an idea of the split between the 4 bulbs which would lower the PAR even more. Each 4 bulb setup ran for 3.5-4 hours per day.

 

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Discussion Starter · #4 ·
Cool thanks guys. It seems to be brighter now actually. Maybe the bulbs needed to burn in a little. I definitely need to replace the 6500k bulbs I got with the light. Was going to get Giesemann tropic, but no one seems to have them.
 
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