maybe try some silky-wave-long-exposure

If you’re doing this on a budget, you probably do not have an ND filter that is absolutely color-neutral. The solution’s pretty simple: a grey card. Take two (or more) shots, make sure one of them has your grey card in-frame somewhere. Then, when you edit, select all the photos you took, go to the one with the grey card, and using your color picker, tell your processing app ‘this is neutral’ — and the color cast from your filter goes away.

Oh, and if you don’t have a cable release, your camera might be able to introduce a delay between when you press the shutter button and when actuation happens. Check your manual. If you have a Nikon, check to see if Thom Hogan has a guide for your camera. Turns out you have a complete intervalometer built in — it’s just not well explained in the Nikon manual.