First time i heard that and i can understand what exactly is your problem. What do you mean reduced , check the content of your sd card , maybe you add a folder or something you download. You mean if you flash other rom , your sd card space will increased again ???? Maybe you confused the internal memory with external. Open root explorer please , scroll down and go to folder "storage" , open it and take a screenshot. Then , go back again and a little higher you'll see a folder "sdcard" , open it and take a screenshot. Upload both screenshots to see them please.
Copy the cwm recovery file in both cards ( external and internal ) and try again , just write the code correctly and you will not having problems.
Open terminal emulator. Write , su ( hit enter )... Then write , dd if=/sdcard/recovery-cwm6036-8225.img of=/dev/block/platform/msm_sdcc.3/by-num/p16 ( hit enter and it will be done in a minute ) Just remember to rename the cwm image as you saw in code ( cwm6036-8225.img ).
Rom manager it will brick your phone or it will damage it .. You didn't flash cwm recovery properly. You must install cwm recovery with terminal emulator. Just read the topic of KonstaT about cwm , at the end of this post describes the way to flash cwm with terminal emulator if your device is allready rooted. Delete rom manager and do not install anything with rom manager on this phone. Are you sure your phone is rooted ??? With which app did you root your phone???
You must install CWM recovery. As you don't install it , then it goes to stock recovery ( android system recovery ). There is no stock rom which include CWM recovery , you must install CWM by yourself. Read well this tutorial ... http://www.modaco.com/forums/topic/365228-recovery-clockworkmod-6036-for-zte-blade-v/