I'm both intrigued and confused! I have never heard of silicate testing being a thing in freshwater aquariums (I'm assuming your tank is freshwater, right?, as you mentioned it being a planted tank).
What was it that prompted you to test your water for silicate and what problem do you believe your current levels are causing?
Out of interest, I just looked up the Seachem test kit here
and I see that it says:
"Natural sea water contains about 10 mg/L as silicate. In reef or other marine aquaria, silicate should be 1 mg/L or less. Silicate is non-toxic to ﬁsh and invertebrates, but is ideally kept below 1 mg/L to minimize diatomaceous algae. In freshwater, silicate is not critical. Usually, freshwater silicate concentrations will range in the area of 4–20 mg/L."
So, according to that, silicate levels don't matter in freshwater tanks and your current ranges are within the normal range anyway!
If you need to remove it, then how about Seachem PhosGuard
"PhosGuard™ rapidly removes phosphate and silicate from marine and freshwater aquaria. Although PhosGuard™ is effective in both fresh and marine water, it will operate better in sea water and the need for it is better defined in sea water. It is not recommended for phosphate buffered freshwater (PhosGuard™ would remove the buffer until saturated). PhosGuard™ is highly porous and bead-shaped to promote easy water ﬂow through and around it, thereby increasing both its efficiency and capacity."
Or maybe not...