"maintain it at" is correct and usable in written English.
You can use it to express that something or someone should continue at a certain level. Example: Make sure you maintain your grades at a high level.
Ridgway updated its master plan in 2000 to control growth and maintain it at 5percentt annually, said Greg Clifton, the town manager.
And the radio said, although the report could not immediately be confirmed, that the cabinet was expected to terminate its unilateral limited cease-fire -- despite plans to maintain it at least through Mr. Sharon's scheduled visit to Europe next week.
"We need to maintain it at any cost.
"For 18 of 19 programs tested, majorities want either to increase spending or maintain it at current levels," Pew found.
Darling promised in the budget to maintain it at £250 to those at least 60, and £400 for the over-80s, until this year.
Some Bostonians, perhaps miffed over losing him, insist he inherited a loaded team and the resources to maintain it at a high level — there was no other way to compete in the same division as the Yankees.
We know that raising a respectable lawn and maintaining it at lofty suburban standards is no easy task.
Newman's class consciousness is no less pronounced in Klinenberg, who maintains it at far greater risk to his argument.
He displays masterly control over the emotional life of the novel, maintaining it at a very high level indeed, and then pushing it at points where the narrative becomes almost unbearable.
It reduces the pressure of a high-pressure air source to the required level for a given pneumatic load and maintains it at a steady level.
Soil analysis of the experimental plots before and after one cropping season indicated that common beans increased N slightly or maintained it at the pre-planting levels.
