I cant get my co2 at level I want. I have a sump as a filter, it is covered. Is there any tricks for setting this right, or should I get a canister filter?

I'm injecting co2 using a DIY pvc reactor. The sump is a 20g tank, flow is about 400gph. The tank is 120g.
I have to do like 15bps of co2 and it's still very low.

Canister will definitely be easier but have you tried TBarr's venturi design? Another option for your setup would be Mazzei venturi.

If you have a reef ready tank with overflows, you need to raise the level of water in the overflows, as the waterfall effect loses a ton of c02. This will help a lot. Use a Durso standpipe or extend the current pipe in the overflow so it is taller and no more than 2-3 inches from the water line. I raised mine from 6' to 1.5' and it is much quieter and the c02 loss is much less.

Please look for my threads on a 180 gal over the last couple weeks, as many have given me good advice for my setup.

I raised the level in the overflows, got better current and flow thru, used the venturi idea mentioned above (not the Mazei), covered the sump, etc.

All have increased my c02 assimilation.

Direct the flow from your reactor into the intake side of the pump to the tank. That will help distribute the c02.

Current also plays a significant factor.

Hope this helps.

thanks. Im actually using an overflow box, so how do I raise the pipe?

Depends on type of overflow plumbing.................

Two options:

1. Replace the ENTIRE intake standpipe in the overflows with a Durso type Standpipe. Google search (Durso Standpipe) on this, but here is one link with a pic...

Durso Standpipes Portal > Home

2. I have a floating type sponge/buoy setup (hard to explain sorry) where I was able to insert a 2" extension piece of 1" PVC (using a collar adaptor) to lengthen the existing standpipe. Length of extension is of course based on size of your overflows.

As stated, I have plenty of posts recently around this, so search for my username threads...

Remember that more water in the overflows, may mean more in the sump, so be careful it doesn't spill over.....

Good luck.

Here is a picture of one of my standpipes. You can see the floating buoy which is seated inside a 1" strainer which in turn is surrounded by the large sponge.
The buoy rises/falls with the water level. The strainer sits in a 1" PVC collar.

Since the strainer is 1" and fits into a normal PVC collar. I just added the extra PVC length and a new collar and extended the pipe. You can see that the waterline is only 1-2" from the overflow teeth.

The PVC and collar directly below the sponge is the EXTENSION. All the rest was there.

Only two pieces of equip:

1" PVC cut to desired length.
1" PVC slip collar.

I cut a few different pieces to play around. Had to buy 10' of PVC whch will most likely last me a lifetime. Let me know if you need any lol

Let me know if this is unclear.

Hope this helps!

Thanks. It is clear I dont know if it will make a difference with an OB, I think I'm gonna switch back to a canister and tehn a closed loop for the co2 reactor.

By overflow box do you mean a hang on tank style one? Thats completely different than the above, but a durso might still be employed.