Dun panic. It is alright to off the lights for one day.
I dun think your ballast can support lights with a higher output. you will have to change the ballast also. Or, you can add two more lights to make up the difference. I think it is better to have a few bulbs covering the lighting needs, cos you get a better distribution than from a single bulb.
Alternatively, you can get rid of the riccia and grow low light plants using your exising setup.
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