If you're on a well, be sure that your well isn't cycling off and on, as that can burn it up.
Add another hose if you have a second faucet and watch your pressure gauge. Try to keep it in a range where it isn't going up and down, but constantly on.
We have a 12,500 gallon pool and I can fill it in 17 hours running three hoses from our 4" 1hp well.
I had a pool just like that....and I built a solar heater just like you did...and it will work.....but....what I learned was...
The water will be scalding hot for the first 40 sec or so..then slowly cool off to just cold, one...the 1/2 tubing we used was to small and doesn't hold a large enough volume of water, two the filter we have pushes the water to fast thru the small tube and it doesn't have time to get hot
I tried a big water feature pump but it also pushed the water to fast....the idea was abandoned because the following year we moved ....
But...I think to make it work ( and it can) you need to either slow the water down so it has time to heat....or double or triple the amount of tubing or both. I figured it would take about 300ft of 1/2 tubing and a smaller pump ( i didn't like having the pond pump in the pool with people in it...as mentioned above...but slow the water down with some type of bypass in the filter pump return line and triple the amount of black tubing and I think it will work...
black hose is from the sump pump to the solar panel, then red hose out to discharge
It was windy, only 25deg out, and intermitently cloudy... so I was only seeing a gain of 2deg. Pretty disapointing, but conditions were far from ideal. We'll see what it does on a nice hot day.
One shocking thing that happened was that my water turned green once I added my chlorine. After a little internet searching and talking to the guys at work I discovered that hard water's iron reacts with chlorine and produces the green color. I tried an HTH product that did noting, then took a co-worker's advice and used Super Iron Out. Cleared right up, but a couple days later it's back. Not sure where to go from here... don't want to keep dumping this stuff in... not exactly meant for this use although my co-worker said he's used it in his pool for a decade. I may take a sample to a pool store and see what they say.
Even more convinced that it's iron after changing the filter! It's completely colored a rust brown. Going to the pool store tomorrow to see what product they've got for this.