Advice and opinions on fertilizer resivor

I'm starting to do more plants at one time , 3 autos , in a 5x5x6. I know I'm going to need at least 4 gallons every time I feed/water. I use an R/O filter system for water but it's small and would take a few hours to get that much water at once.
So I came up with this idea. It's a 7 gallon container I put a spout on and locking lid. There is no direct sunlight it's actually dark unless I'm in the room with the light on.
I got a pond pump rated at 480GPH and inverted one of the "bell" style fountain sprays to circulate the bottom and prevent settling. One problem I'm running into it s keeping the pump in place. I'm onpe to any suggestions or advice. I'll answer any questions that may come up.

If I understand correctly, you are using the pump to aerate the reservoir? Why is the pump moving within the reservoir an issue?
I use a 55 gallon poly barrel for a RO fresh water reservoir. Air pump for aeration and a aquarium UV light for sterilization. Light from the grow can penetrate the white plastic enough to form algae so recommend panda film wrap or some other method to block light to reservoir.
What is your grow type, soil, coco, dwc, etc.?

Ok I can wrap it later today , I was using the pump to prevent settling on the bottom. It's only gonna be in there 2-3 days between feedings. Sometimes it gets in a spot and starts vibrating on the pipe and bucket , weighing it down would keep it a little quieter and my cats would leave it alone .
I do a custom soil mix with outdoor garden soil , coco , perlite and worm castings. Then spay the top with Neem oil to prevent fungus gnats.

Can you suspend the pump from the lid using tie-strap or maybe just take the loop out. Just use the pump, laid on its side, for adequate circulation.

Not sure how big your pump is weight wise, but I use a small pump 460 GPH in my Flex reservoir for my Autopots. I have it on a wifi switch that runs it for 5 to 10 minutes 3 times a day automatically. The switch cost me $8.00. I purchased some 1 inch round earth magnets off TEMU and glued one to each foot of the pump and placed it against the sidewall inside the reservoir, I then used the other magnets to attract the magnets on the feet of the pump from the outside of the reservoir to anchor it to the inside wall. Never moves.

Sorry y'all my engine blew the other day and have been scrambling to get a new one since. I appreciate the response's and will look to see what will work best.