I know that space is big and satellites are small compared with the moon, but do they have, or will they if we get more, any effect on the sea and ocean water on the earth?
Yes, but the effect of any plausible number or mass of satellites will be negligible.
The force due to gravity between two objects is proportional to the masses of the two objects and inversely proportional to the distance between them. The mass of the Earth is constant, so the things that matter here are the mass of the other object, and how far away it is.
Large satellites mass a few tonnes, while most are lighter. The mass of the moon is 7x1019 tonnes.
The moon is further away, which weakens its effects, but only a few hundred times further away. So the effect of the moon will be somewhere (very roughly) around 1017 times that of a single satellite.
So unless we were to launch literally trillions of satellites, we can continue to treat their effects as negligible for most purposes.
(it is a bit more complex because of the question of how these satellites are distributed - some of them will cancel out others, and so forth - but the forces will be so small that I don't imagine it matters)