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i'm getting ready to set-up a 75 gallon plant tank. i recently purchased a 250watt metal halide clamp light to light it. i have 5 small altums in a 29 gallon that i'm planning on putting in the 75 gal. by themselves with lots of plants, that was the plan.

would this tank be too bright for altums? do i have to inject Co2 with this much light over the tank? or could i cut down on the daily "on-time" and do low tech with amazon swords etc. etc.

what plants would be good choices for floating on top to block some of the light getting to the tank? i believe i oversized the light and would have probably been better off with a 150 watt clamp light. any suggestions from the experts would be appreciated.

sincerely, john
 

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Honestly that might be too much light, it works out if you follow the watts per gallon suggestion, but with the intensity of MH I wouldn't be surprised if you're fighting green dust algae the entire time. A 48" T5HO fixture with 2 bulbs would work fine, one with four bulbs and two chords would give you the option of noon-blasting the tank for super growth. If you have a canopy, you could mount a few AHsupply bright kits in there for around 2 to 3 WPG. In any case you will need pressurized CO2, no doubt, unless you cut down below 2WPG. Floaters would definitely help, I would use azolla, giant duckweed (Spirodela polyrrhiza), and ludwigia sedoides.
 

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Running 1 MH light you'll have extremely bright light under the bulb, and almost no light on the ends of the tanks. You may also have heat issues in the summer. I also would go with a 2x54 watt T5HO fixture if you aren't going to inject CO2, and a 4x fixture if you are.

You'll probably also need to raise the fixture off the tank 6-8" if you're not injecting CO2.

Pistia is probably my favorite floater. Red root floater also is up there.
 

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Personally I would also use the 2 bulb even with CO2 injection. This is coming from a person who's already had their fun clipping crazy plumes of plants once a week and trying to keep ferts in balance. The CO2 would still create lush growth, and with the lower light level it would be much less of a tight rope walk trying to keep CO2 levels up and ferts in balance, any wavering of that stuff would have less of an impact with less light, or a slower impact which is easier to get under control. High tech tanks become more of a headache as the light increases, more fun for a select few but more headaches for me. :hihi:
 
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