I'm not conversant with Solar powered pumps as I have a mains powered pump in my small garden fountain controlled by a mains timer switch.
However. I am aware that the pumps can get blocked up as my pump is in the bottom of the central column of the fountain and the water enters through two square holes, taking the bird muck, algae, etc with it.
I found that by blocking these two entrances with sponge pads, it kept the pump clean for much longer and didn't interfere with the water flow.
Also, I put some bi-carbonate of soda in the water which helps to keep the algae under control and doesn't seem to affect the birds drinking habits.
Hope this helps.