What are your test results, and what test kit are you using? How have you been adding chlorine?

If the problem IS filtration, then getting these cartridges will help:

Get TWO -- these cartridges are MUCH higher quality than the OEM models. And CHECK first, to make sure you use the Intex "A" or "C" cartridge. If not, tell me what you use, and I'll try to find the right cartridge. Let me do it, though - most of the "Unicel" cartridges being sold on Amazon aren't actual Unicel.
Unicel C-4607 Replacement Filter Cartridge (Easy Set Size A or C) @ Amazon @ Amazon
Unicel C-5315 Replacement Filter Cartridge for 15 Square Foot Intex B Filter @ Amazon