Several agriculture fertilizers incorporating P2O5 as P source have been successfully used since long to grow Microalgae. So, I do not think you may have any problem with your Chlorella.

The main phosphorus uptake source is HPO4 -2 (phosphate) through phosphatases. Since P2O5 can be reduced to PO4 -2, you can try with a P2O5 source.

I think you won't have problem with P2O5. There are successful examples in the literature (e.g. doi:10.3390/app10113890)

It is convention to express the phosphorus(P) concentration/content in fertilizers as P2O5, oxide form of P.Plants absorb the P in ionic form as H2PO4 and HPO4 form, mostly as H2PO4 form. You can use calculated amounts of any of the water soluble P fertilizers as per requirement in the experiment as source of P to plants.

Thank you! Jose Pedro Canavate Hashem Asgharnejad Annangi Subba Rao

My experiment shows that it works fine! however, I am not sure if P2O5 is really the phosphate form in fertilizer.

I have read recently read questions related to this in research gate, and some said that P2O5 is only how they state it in fertilizer packages..

for Annangi Subba Rao , does it mean I am supposed to measure the PO4 content in the medium after I mix it?

H2PO4, HPO4 ( soluble) or PO4 (insoluble) forms of P are present in fertilizers but the P content is calculated and expressed as P2O5 content by fertilizer companies.While measuring P by colorimetric methods, H2PO4 ion participates in reactions and is actually measured . But the measured H2PO4 concentration is expressed in terms of P (elemental form of P is not measured) for both available P in soil and plant uptake P.

The dominant forms of Phosphates in solutions depend on the pH value of the solution. What will be the pH value of the of the material (soil) in which you cultivate your crop?

The answer is very simple. No, they cannot, because fertilisers do not contain P2O5.

To read more about this, check this Editorial: Lambers H, Barrow NJ (2020) P2O5, K2O, CaO, MgO, and basic cations: pervasive use of references to molecules that do not exist in soil. Plant Soil 452: 1-4