too much & not enough algae

I have 5 golden barbs & 2 small otos in a 12 gallon tank (tank fully
cycled, never goes beyond zero for ammonia or nitrites at this point).
When I first set up my tank, I got brown algae (apparently typical in
new tanks) which the otos gobbled up. Then I had little to no algae,
and my otos never took to either the blanched zucchini or even the
algae (Hikari) disks I put in there, but the piggish golden barbs did.
The otos seem to like "vacuuming" the leaves, gravel and tank walls
and nothing else. And they seemed bare.

About a week ago, I went out of town and added some phosphate-based
buffer to increase the algae in my tank, on purpose, to feed the otos.
When I got back, the water was GREEN....one-celled algae organisms. At
this point, I'm worried:
1) the floating one-celled algae are not edible by otos; they need
stationary types of algae
2) the green water algae is using the light and nutrients in the water
that could be used by either the plants in my tank, or the algae that
would grow on them (food for the otos)
3) even with a bubble wand, the algae & its eventual decomposition
would eat up lots of oxygen if I tried the 4 days of darkness for the
tank, and there would be even less for the otos to eat

Few questions:
1) What is an oto-specific food source? The Hikari algae discs have
some krill & other meat sources, so my hungry golden barbs attack it
before the otos even see it. The otos don't seem to like blanched
zucchini or lettuce. Any way to grow stationary algae without causing
a green water algae bloom?

2) How to get rid of the green water with minimum stress to my fish &
specif otos? One of my otos died before, I think either due to
starvation or stress. I don't want to repeat that again. So far, I've
been doing 25% water changes every day, to slowly remove the
phosphorus I added (I think the "fresh nutrients with tap water" is
bunk, unless you have phosphates in your tap water, which is
exceedingly rare nowadays). When I had no phosphates, but some
nitrates (from the nitrogen cycle), my water had no green tinge.

Thanks!
Jason