1. Use polyquat initially, instead of chlorine (info, below). It will keep your pool from turning green, and will help filter the iron, etc. Once the pool is full, add very small doses of chlorine, gradually raising the chlorine level.

2. Make sure you are cleaning your cartridges properly. Links and info below.

Ben
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+ Chlorine is the strongest algaecide you can buy . . . but occasionally, you may need a different one. Almost the only alternative algaecide we recommend is polyquat -- poly [oxyethylene (dimethyliminio) ethylene (dimethyliminio) ethylene dichloride] . This product is a GOOD clarifier and a moderately good algaecide, with almost no bad side effects. We often recommend it for use when you are going on vacation, or when you need to lower your chlorine, to prevent remove stains. It has become quite difficult to purchase locally at the normal full strength 60% concentration. If you find it locally, at a 60% concentration, that's fine. But be SURE to check the chemical name. If you need to buy it online, here's an Amazon link:
Kem-Tek 311-6 Pool and Spa 60-Percent Concentrated Algaecide, 1 Quart
+ The OEM cartridges in Intex / Summer Escapes / etc. filters are not high quality. The Intex manuals recommend replacing them completely every 2 weeks. A BETTER option is to replace them permanently with 2 - 3 Unicel cartridges, and rotating them through a cleaning solution. Properly maintained, the Unicel cartridges will last all season AND will filter better. So even though they cost more per cartridge, they cost less per season! Learn to maintain them, by reading this post, Cleaning-your-Cartridge-Filter-wiithout-Damaging-It!

But, purchasing them is tricky. Amazon does not consistently stock them, and some of the 3rd party sellers are charging high prices and/or high shipping. So, check the Amazon link, but watch out for the prices and shipping costs.

It would be nice if you could just buy them elsewhere, but many of the online pool stores are listing Pleatco or other Asian made low quality filters, as "Unicel C-4607 type" or "fits Unicel C-4607". So shop carefully!

Here are the Amazon links:
Unicel C-4607 Replacement Filter Cartridge (Easy Set Size A or C) @ Amazon
Unicel C-5315 Replacement Filter Cartridge for 15 Square Foot Intex B Filter @ Amazon