to siphon the gravel bed.

[Jack]

Unless you are using coarse crushed coral you shouldn't need to siphon your sandbed. You're probably doing more harm than good, which is proven with your diatom blooms.

Brisk circulation should prevent most detritus settling in your reef. Maybe try out a small AquaClear mechanical filter to polish your water but just make sure you change or rinse the floss/foam very frequently to prevent a "nitrate factory."

If you're still worried about detritus a small cleanup crew wouldn't hurt. Hermits and Cerith snails are great sandbed cleaners.

But, obviously you've found out that messing with the sandbed disrupts the tank and causes a diatom bloom... so stop. You'll be fine with just plain water changes.

Hope that helps.