Having an issue getting our pools temp to and above 70. 22x52 intex ultra frame. Sees sun morning and mid day then starts to get shade from about 2:30-3pm. Right now a heater or solar cover are not in the budget. Also doesnt help that our daytime temps are between mid 70's to low 90's but most nights it drops to the 50s-60s. Any cheap way of keeping it somewhat warmer?