You might be able to run the two LEDs in parallel and cut the current they use in half. That would get it down to about the right level.
Normally you don't want dissimilar LEDs in parallel but it might work depending on the throw of the dice. The good point is that since these LEDs can handle one of your drivers alone if these LEDs don't balance well nothing will be hurt.
Even if the drivers don't have a dimming circuit they should have a current adjustment pot internally that you should be able to turn down to make them less bright. It may not have enough adjustment but it could help.
You can shade the output of the lights by using some plastic window screen or eggcrate.. Untill you figure out if you can add a potentiometer to dim your drivers. Just put two layers of screen under the lights.. Run a test not installed on the tank to make sure the beam from the lights doesn't melt the screen. I read stories of guys burning the table or floor with LEDs directly on them left on for only a few mins. Good luck.
Thank you guys for all your help, i think i may try with a frag offa my purple acro to test before i do anything else to it. One question as i am a complete noob here, in paralell i would be hookin both hots to the driver and both negatives to the driver?
Ok so o reread that, how or is there some kinda caculator to figure out what size rezistor to put in it? Say drop it from 900ma to say 700 ma ?
I did not get your parallel question. You may need to rephrase it...
As for resistors for fixed dimming there is no "table" but if you can tell us what current you are running now and the actual voltage across each emitter we can do some math and tell you what resistors to get.
If those two measure exactly the same, then you should definitely try running both LEDs in parallel on the same driver. Especially since you have everything terminal blocked. See what you think. That will still be a heck of a lot of light for that tank.
As for shunt resistors:
I don't know what your math was...
You have a current source. that will supply 900mA thru whatever load it's driving. The resistor's duty is to pass 200mA if you want to reduce the current that would otherwise pass thru the LEDs.
8.95V / 0.200A = 44.75 ohms
This resistor dropping 200mA will dissipate:
0.200A x 0.200A x 44.75 ohms = 1.79Watts. Make sure this resistor is rated at 5watts or more of power dissipation.
Caveats. Since this shunt resistor will cause less current to flow thru the LED the operating point will be different which means the voltage will be different which would change the resistor value a little. The result is you will need to adjust the resistor a little from the computed value above.
Set it to about 44 ohms then measure its resistance. Install it across the emitter. Power up. Measure the voltage across the resistor and using ohms law compute the current thru it. If you don't like the result POWER OFF and then re-adjust then power back on. Step and repeat. NOT following this procedure may likely blow your emitters.