Algae won't stay alive

My tank isn't completly cycled yet it's been about 20 days. I have two questions. On October 8th I tested my stuff and had levels like this.

Ammonia >8 ppm
Nitrite 5ppm
Nitrate 10ppm

Today (Oct 11th), just 3 days later I tested my tank and got

Ammonia 0.25ppm
Nitrite 1ppm
Nitrate 10ppm

So my question is how could this happen so fast? Could my tank just start cycling so fast all of a sudden?

My second question is why won't the micro algae in my tank stay alive? It keeps dying off. I was told before that it wouldn't stay alive while the tank was cycling but I have measurable amounts of Nitrate now so shouldn't this be enough to feed it?

 

I'll answer the second question first: Please forgive me if I'm too simplistic, but it's late and I'm not going write a master's thesis here, and you probably don't want one.

The algae needs water, light and something to eat. You've got the first two. Generally, algae feed off of nitrates and phosphates in the water. Also, the types of algae will compete with each other for the available nutrients in the water column and on the rocks and sand.
My guess is that you have minimal phosphates, so your algae bloom, and then die. Once they decompose, a new batch blooms, and then dies. If you measure the phosphates, they'll probably be at zero unless you're at the end of a "bloom-and-die" cycle.
As for your first question: The difference you see is because the nitrogen cycle is a curve, not a straight line. The bacteria involved in the nitrogen cycle are increasing in numbers logrithmically.

 

Woot. Soooo... I'm guessing that my cycle is coming to an end soon? Am I right? It'll be a little early. Shouldn't I add a fish now so that there is something for the denitrifying bacteria to eat? As opposed to waiting till Ammonia and Nitrites reach 0.

 

Wait...... also what produces phosphates then?

 

Rot. Disolved organics in abundance I would guess. Overfeeding. Leftover nutrients in the water.

When the nuissance algae dies, boy does it die. It's like it wasn't even in your tank in the first place.

 

Bottom line is you are really rushing this tank and the fuge is going to probably be far to vast in its total volume to run very well on a 75 gallon tank. I think you have the fuge at 36 inches ? With a tank this new you have nothing to feed the algae just as the person above mentioned they need Light food and water and they have no food a Fuge really should be added after the tank is up and stocked unless you want to add some fertilizers then they will just starve out..You would be better off just setting back and letting the system to fully cycle.