Try to swap the driver for testing.
If both driver has the same issue, then mostly likely is the LEDs issue...
If the driver swap to the white string LEDs also have same issue, then is the driver issue.
The voltage measure should be the same as the stated on the driver...
If the voltage is not, probably there is a short or the current is to high...
Measuring current is not so straight forward...
Are they connected to the same driver?
How many driver you have..?
You may tried to swap the driver and see how it goes...
The LEDs are fine...
Is just that the voltage output from the driver is too high.
Can you measure the vout?
Are there any LEDs which seems brightness not similar or any shorted wire?
If is the ballast, you may need to check whether the ballast is dual channel or single channel.
If dual channel, you would need to replace the entire piece which is slightly more expensive than single channel.
Based on the tank dimension, probably you can have a gap of 2 ~ 2.5 inch with lens of 60deg.
If my comment above is not correct, DIY gurus, do help to comments.
Thanks.