DWC High PH in Rez After Algae Growth

Hey guys, having some serious issue going into flowering that I'm helping someone can help me with and save my crop!


I have a DWC setup that has a large 4x4 tray which houses the route zone of the 25 plants I have and a rez that the water from the tray drains into a recirculates. Everything was going fine as usual until I accidently left part of the root zone exposed to light for about 6 hours when I was switching out the rez from veg to flowering and starting my 12/12. (was in a bit of a rush, stupid I know)

SInce then a massive amount of what looks like brown algae has grown in the root zone and totally coated the bottom of the tray causing my normal 5.8-6.2ph to sky rocket to 8+. I have since cleaned out all of the algae and dead roots. and flushed the entire system again cleaning all parts, tubes, drains, pumps, rez, etc. I then refilled with water and added my flowering nutes only to find the PH still sky rockets but I don't see algae any where in the system and now can't figure why it's still happening.

Here is what I have

400 watt MH for Veg
1000 watt HPS for flower (just switched to flower)
25 gallon rez w/ 10 gallon tray
Full line of Aqua Canna Nutrients with subculture B and Calimagic.
Additivies include Snowstrom ultra and I did use the last of my bushmaster.
RO water - tested and good
1 x 4 watt air pump with one 18 inch flexiable air stone. I was running this on the lowest settings 24/7 during veg without problems. I am running the pump for 15 on 2 hours off now on the lowest setting.
Rez temps = 69-71F with Air temps 68-75F

My issue is there is no visible algae left, I don't see or smell any root rot. The roots have a slight brown color to them but thats normal with the Canna line a couple of them stain the roots.

Ph is currently 8 and I cannot get it to drop. I have already done 2 full rez changes.

Any suggestions would be welcome! Thanks.
 
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