My problem is that when I slap, I get a harmonic instead of the deep note Im trying to get. Is this a problem of my action is too low, or is there something Im not getting. I can do pops on my index finger all day long so thats not a problem.

Is it a 2 octave neck? Seems to me when you slap a 24 fret neck, the open string wants to play the hamonic. I don't have that problem when slapping a fender jazz, or other 20 fret bass.

Try it on some other bass, if the problem persists try playing farther away from the neck you are hitting a harmonic "sweet spot". Maybe slaping harder will make this go away

Make sure you are not on a nodal point that produces a harmonic. It is also important that you are bouncing your thumb off of the string as if you were touching a hot stove. If your finger is in contact with the string too long, it could cause a harmonic to sound.

the whole 2 octave neck thing holds no water.

it has to do with your right hand technique and where you're slapping.

try moving around you'll figure it out.

I addition to what others have said I find that the "bouncing off" slap method gets more high end than the bassier sounding "string through" method where you slap through the string to rest on the string below (like the downstrokes in double thump).

Almost every student I teach slap to has this problem at first. It's not really about where you slap the note. The problem is that you are probably hitting into the string. In either slap technique contact time on the string is the key.

When you are using the "bouncing" thumb technique, your thumb needs to relax once you start the motion and allow the natural rebound of the string to make your thumb bounce off. Much like when you are hitting a drum with a drumstick. If you hit into the string you are going to choke the note and cause harmonics to be played.

With the "string through" approach you should be using a similar approach only this time you are kind of flicking the string on the way through.

The main thing that causes you to hit into the string is being too tense and also hitting too hard. Slapping is not about how hard you hit the string. Try practicing some simple slap exercises like playing 8th notes at about 120bpm and hitting the notes softly until you get used to the motion.

Use a scrunchie at the nut (like in the picture). It'll keep the harmonics from ringing out, no matter where you hit the string. It will also keep unwanted resonance from the B or E string.

Use a scrunchie at the nut (like in the picture). It'll keep the harmonics from ringing out, no matter where you hit the string. It will also keep unwanted resonance from the B or E string.

This won't solve the problem if it is caused by hitting into the string. Also why not just learn to use better muting technique. What happens when you want to play harmonics on purpose or play an open string?

What happens when you want to play harmonics on purpose or play an open string?

Then you move it past the nut. It works for me and I do use the proper technique but sometimes it's still there, especially with new SS strings. It works fine for me. The scrunchie doesn't dampen the whole string from vibrating. It just dampens it enough to get rid of all the unwanted resonance you don't want. The more you play with it, the more you learn how to use it to your advantage. I play open strings all the time and some harmonics and it really doesn't affect my tone as long as it's just over the nut. Any further up the neck and you will run into problems.