Dolphin M400 or S300i


Well-known member
Apr 7, 2013
So I have given up on the old Aquabot Supreme after a couple repair attempts, she just keeps spinning in a large circle and I do not want to dump any more money into her (Sally).

I spoke to Marina Pools in CO and I am between the M400 or the S300i. My pool is 40 feet long, 20 feet wide in shallow end and 16 feet wide in the deep end, 8 feet deep to 3.5 feet deep, main drains in deep end floor, free form liner with wall seat in middle of pool.

What are your recommendations on pool robots.



Mod Squad
LifeTime Supporter
Jan 17, 2012
Evans, Georgia
How close is your outlet to the pool? Will a 60' cord allow the cleaner to hit all points?

I also vote for the S300, but some haven't been thrilled with the bluetooth on the i version. Just a warning. Otherwise I sort of wish I had some of the features of the S300 on my S200.

Maddie :flower:


Mod Squad
Gold Supporter
Platinum Supporter
LifeTime Supporter
Jul 16, 2012
Central MD
Do your main drain covers protrude up a lot from the pool surface? Some have trouble with the S series getting high-centered (stuck) on them. The M400 has a 3 brushes, including a center one which allows it to traverse main drains without getting stuck. Our S series clone gets held up on our covers but always frees itself withing 30 seconds. But it wouldn't take much more height for ours to be a problem.

S series baskets work really well, especially with the dual filtration setup.


Bronze Supporter
Jun 20, 2016
I have an s300i. I have raised drains. 90 percent of the time he gets himself out of trouble in his own. I really like the basket like others have said. Cleans up so easy after each use.

Bluetooth. So hit and miss. I can’t stand waiting for it to find itself and log on I just hit the button to let it go for 2.5 hrs.

I wouldn’t use that to defer you. I love the bot. I like the way it uses water to hold itself to the walls and move vs the floats on the m series.

I had just mentioned on another thread that they r moving towards the s series tech vs the m series. The new m600 uses that tech. I don’t even know if it’s out yet.

I would buy my s series again no questions.


Gold Supporter
Apr 3, 2019
jimim, great point - they new M600 (see here
) that is coming in June (rumored) is going to be a combination of BOTH. I have no idea when this thing will come out or what the price will be, but it has all the same features of the 300i in terms of phone connectivity. You can definitely tell that Dolphin is moving away from the M series design type with the floats and most of their latest tech uses the S series (or an evolution there of) tech/body style. My vote is an S300i if you have to have it NOW or need something with a proven track record and all the bugs worked out, or an M600 if you can wait for the new tech to come out and are OK with taking a risk of being a guinea pig. Call Dolphin to confirm when/if this thing will actually arrive for sale and what the price is. I think it has been delayed because of software issues (so that's another concern with a new product).


Silver Supporter
Jul 2, 2017
Thornton, PA
I too was torn between the S300i and M400. I ultimately went with the M400 after talking with Marina as were afraid of it getting hung up on the drains and they recommended the M as well for slight build quality favor. Ultimately I think I would have been happy with either. The M400 cartridges took a little getting used to but no problems at all once you've done them once or twice. I've done 4 cleanings now and no issues cleaning over the drains, sunshelf, walls, or spa. I'm happy.

Also agree the bluetooth/app pretty much sucks and I won't use it much.


New member
May 25, 2019
North Carolina
I'm a new, first time pool owner (we closed 5 days ago) and I'm still trying to figure all this pool stuff out. After trying to brush and use the suction vacuum to clean the pool today, we decided that a robot cleaner might be the way to go and, from what I've read on here, it sounds like it is a wise decision. In researching them, the Maytronics website says the M400 has "fine and ultra-fine filtration." Does it pick up larger debris, like small twigs and leaves, from the bottom of the pool as well or just smaller debris? Would the basket filter on the s300 be better for that application? Does the s300 still clean up algae like the m400? Thanks for your insight!


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

Welcome to TFP.. a great place to learn how your pool works... :shark:

The M400 and S300 will both pic up the same type of debris.. Robots are designed to pick up "stuff" that falls into your pool.. While they may pic up dead algae, that is not their primary job.. You don't get rid algae by filtering with the main filtering or a robot... If you have algae, that is a chemical problem, not a filter problem..

I suggest that you read though our Pool School and this link... ABCs of Pool Water Chemistry and see what we are all about..

Thanks for posting,

Jim R.