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Lots of good threads here about bottom aeration. In your case bottom aeration is going to be the best as it is not going to add OXYGEN, but with proper set up you are going to LIFT WATER up from the bottom. You do that by getting a very well designed membrane diffuser that has micron size slits that produce millions of tiny bubbles. The millions of bubbles lift water and create that upwelling of the stagnant water at 20' depth.

My brother-in-law has about the same setup as you, similar pond size, similar depth and he used fountain aeration and got no where with water clarity or algae control. His center hole is closer to 30 feet deep. He finally got bottom aeration and in one season the difference was like magic. Organic matter gone, sand was showing in the shallows, water quality better, less algae, etc.

He had his membrane diffuser in the deep but if you choose to do that you have to be very cautious about starting it up slowly (meaning 15 min run, next day 20, next day 30 etc.) You have 'bad water' at the deepest spot and you want to mix that up into the 'good water' slowly over time. It is better to do that mixing in the spring where water temps are cold and oxygen carrying capacity is high anyway.

Others are better at aeration questions, but they may advise running it at about 10-12 foot depth rather than at 25 foot depth. This would also be true if you are trying to get away with one aeration station placed in your pond rather than in 2 locations. Going to about 12' means you'll get good mixing at about the thermocline and you will push that water movement up into the shallows too.

Since you have weighted line and pump already you can easily purchase 2 vertex brand membranes (very good membrane, very small pore size for millions of bubbles) and pipe them together with membrane heads about 15" apart and figure out some way to attach them to a tote, or a flat cutting board, or some other wide base that won't tip over as it is lowered down. Most find it is best to have the membranes about 24" off the bottom to avoid stirring up the bottom (so you would place at 14' if you want aeration at 12' depth). The further the horizontal distance between the diffuser heads, the deeper the diffuser station goes, the shallower you have the station the closer together the heads are.

Soaker hose makes bubbles but not enough to lift water. A good membrane diffuser makes a rolicking 5' wide boil at the top of the water and that boil is not so much AIR as it is water coming up from the bottom mixed with air. This is the key to success.