your thoughts on my new system plans - please

[profire31]

Before I complete building this years additions to my system I'd like to ask you guys what your thoughts are.  I run a 2 tank (4' x 8') closed system.  This years upgrade is a concrete vault that will house the course filter, bio filter and extra water.  What I have figured thus far is I'm running right at 100 gallons per tank that drains through foam mattress material for the course filter.  From there onto approximatly 100-120 cubic feet of oyster shells (like 10 bushels) and back through the system.  The vault will hold an additional 200-250 gallons of water.  This will give me a total of 400+ gallons to operate with.  Now I know there are several other vital parts I can add but this is what the plans are for this year. 

On average I add 30 to 50 peelers a day and about 80% make it.  This was accomplished without any filter, changing water every 7-10 days and the system operating on 300 gallons of water.  While the I dont think the 80% is too bad I'm hoping to improve that percentage and hopefully make the water changes less frequent.

Thanks to all who reply for any insight you can give me before I start pouring concrete. 

[capt. ron]

i think your loss is to high.  Maybe at the most 10%.  Could be a number of things.  Sometimes the crabs are weak just comming from low oxygen water.  High water temps, high air temp, dehydration.  I think you're changing your water to much.  I rarely change mine.  Just add a few gallons of water a little salt and sit back and watch 'em shed.

Ronnie

[rdbeard]

Also ,try keeping peelers that are more rank. studies half shown that the longer a peeler is in the tank the higher the chance of dying and causing others to die. Br. Breeze on this forum could give more insight, i believe he had some bioligist study his set up last year or the year before.