How much lower is the end of your siphon hose? The lower the end of the hose the faster the flow. I run one of my hosed down a flight of stairs and out the front door, it flows super fast. Also the larger the hose diameter the more flow. When vacuuming the sand, if you hold the vac above and kind swirl it around the stuff on the sand will move making it easier to catch in your tube.

 

I also run my out the front door in order to give it more of a drop off for better suction. Although, I never thought about the diameter of the hose - good point.

 

You need a vac with larger hose like matt said.The vac tube doesn't need to much bigger, but the hose from it is what makes the diff.

 

Oh... Its just a little shop bought thing. Has a large vac chamber but the hose just reaches from inside tank to bucket on floor next to it... None of this down the stairs business!

 

Good advice so far.

Also, if you don't want to increase the size of your entire hose or you don't have a way to increase the amount of drop from end to end, either buy another short gravel vacuum with a smaller ratio of vacuum to hose or adjust that short one. (By short one, I mean tank to bucket) Use the short one for gravel vacuuming and your long one for water changing.

Alternatively, you could just use a piece of hose with no gravel vacuum for those stubborn pieces of mulm that are attached to pieces of gravel. However...

***WARNING*** It will suck up gravel and small fish
Not a biggy, as they are going in a bucket where you can rescue them, but it is best to avoid that by:

1. Place your finger over the outlet end to control flow.
2. Pinch the hose to control flow.
3. Attach a shutoff valve to the hose to control flow.
4. Hold the hose just above the gravel to grab everything you want, but not the bulk of the gravel. When you dump the water, if there is any gravel in it, just empty the last dreggs of water into a net to save your gravel. Fine sand...um... try not to grab too much. Nets won't catch it.

You'll soon master exactly what technique works best on each tank.