It's Green, but WHY?

[Rookie]

28K inground gunite pool. Chlorine on high side for 5 days. Pool showed green tint 2 days ago, progressed 1 day ago, green this morning (can clearly see main drain). Vaccummed signficant brownish powder off entire pool surface this morning and brushed afterwords. Just tested with Taylor K-2005 showing the following results:
FC - 9
CC - 0.5
TC - N/A
pH - 7.4
cya - 90
Alkalinity - 180
Ca - 400
Super chlorinated 5 days ago, 3 days ago, and 1 day ago. Pool has been very difficult to keep balanced all season. SE Michigan.

Your comments/questions/suggestions are greatly appreciated!

[PoolDoc]

Read the Best Guess page, linked in my signature. That will explain the problem. ASAP, add a 10 ppm dose chlorine, using 5 gallons PLAIN 6% (chk %) household bleach to your pool. You probably should buy 20 gallons.

Also, get a cheap OTO test kit, when you are buying the bleach. You'll need to order a K-1515, to make up for the K-2005 inability to measure higher levels of chlorine, but in the meantime, simply keep your chlorine in the DARK yellow to yellow-orange range -- this is NOT a color shown on the tester.

Continue adding 10 ppm doses EACH evening. Brush the pool carefully immediately after the 2nd 10 ppm dose. Add 2 more gallons after brushing.

Amazon link => Taylor K-1515 (Taylor K-1515 FAS-DPD http://www.amazon.com/exec/obidos/ASIN//B003V4YZEO/poolbooks)

[Rookie]

I've added the chlorine and brushed as suggested. Looks like I will be purchasing additional bleach in the morning!! Thanks for the support.

I'm having difficulty locating the "best guess" page linked to your signature.

Thoughts?

[PoolDoc]

It's one of the links in the navy signature bar all the moderators and I have. But here's the direct link:
http://poolsolutions.com/gd/best-guess-swimming-pool-chlorine-chart.html

[Rookie]

We are on day 2 of super shock treatment on the pool. When testing the chlorine it's an deep yellow/orangish color. Seeing some very mild improvement.

What are your thoughts on iron in the water? Is it possible my sand is bad in the filter? I ask because a contractor was at the house today (he has a pool himself) and said it looks like an iron problem compounding the algae bloom. Starting a countdown for fall in MI!!

[PoolDoc]

When testing the chlorine it's an deep yellow/orangish color. Seeing some very mild improvement.

+ What are your thoughts on iron in the water?

+ Is it possible my sand is bad in the filter?

=> Orange tinted yellow is GOOD, given a CYA=90.
=> It's entirely possible to have both iron and algae. This is not desirable, since the algae clean up will tend to cause the iron to stain . . . but you have to get rid of the algae first.
=> Sand doesn't go 'bad', but it can get all gummed up (rarely) or get blown out during backwash (common) leaving you with a half-filled and half-working filter. If you can check your filter's interior easily, do so.