I assume being a 55gallon that you have two 18" bulbs- one for either side.
If so- 2x17 watts = 0.62 watts per gallon... this is about what I have on my 55gallon. Terrible for plants which require high light but it doesn't mean you can't have a planted tank.
I can give you first hand experience how plants will do with that level of low light.
I have sand root tabs, leaf zone, and a single bottle of DIY CO2 (figured any more CO2 would be overkill with my low lighting).
I am successfully growing Java Fern, Java Moss, Star Grass, Bacopa and Water Wisteria. These 5 plants are thriving.
These have all grown and I've had to prune back the Bacopa and Star Grass about once a month or so. Java Moss double in size in 2 months- Java Fern has grown slowly but is healthy and producing plantlets.
(Water Wisteria intially died off to almost nothing- but then came back with a vengence and is my fastest growing plant now).
I've got Marimo Moss balls- but they don't seem to have grown any- not that they would have yet- they grow very slowly.
Amazon Swords are supposedly low-light plants- but that wattage is too low for them. (if my experience is anything to go by)- I've had little success with swords.
Moneywort doesn't seem to thrive either- although it's not dying by any means. It's stating about the same size with very minimal growth. Add to the "surviving but not thriving" category: Pearlwort (HM is the common abbreviation of the scientific name which I forget) and Guppy grass. These plants are both healthy but not really growing like they're famed to do. The Pearlwort came as part of a bundle- I'm aware it is one that wouldn't be expected to do well in low light.
I have a tiny strand of Anarcharis that came with a snail shipment and I planted- it's trippled in size in the 2½ months I've had it.
I, personally, am going to upgrade my lighting because I want to be able to grow more plants- and have healthier growth on the ones I have... but I hope what I've written above is of some use.
There are actually quite a few plants that will grow under low lights... but you're never going to have the same range those with high-light have. Low light will also cause them to grow slower. I'm doing pruning about once a month- high-light people with CO2 and the fancy ferts are at it every week!
