It's Green, but WHY?

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!

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

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?

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-gue...ine-chart.html

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!!

Quote:

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Originally Posted by Rookie

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?

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=> 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.