July home prices showed the first signs of heading down again as the spring and summer selling season ends, according to analytics firm Altos Research. Earlier in the year, Scott Sambucci, vice president of market analytics at Altos, gave a presentation detailing future volatility in home prices, what he called a “catfish recovery.” Sambucci said as the market moves into the next cycle, prices will fluctuate between new bottoms and new surfaces, as historical data shows. The Altos 10-city national median price began heading down from the uptick measured at the start of the buying season, dipping to $450,176 from $450,894 the month before. Prices dropped in seven markets, “a significant change” from the only one to show a decline the month before, which was Las Vegas. “Home prices nationally responded well to spring-time demand and ultra-low interest rates,” Altos said in a report released Thursday. “Now as the summer ends, housing demand shifts and prices will decline to bump along the bottom of the pond again.” Recent data from another analytics firm Clear Capital showed the uptick in prices over the spring and summer months actually failed to offset the downturn measured in the winter. Meanwhile, inventory is adding up. According to Altos, the amount of homes reaching the market increased in 20 markets with the largest increase of 4.89% occurring in Boston. Nationally, inventory increased 5.03% over the previous three months. “In addition to the first signs of prices changing direction, 20 of the markets in this report reported rising inventory this month,” Altos said. “The loss of momentum from the spring and summer markets is confirmed.” Write to Jon Prior. Follow him on Twitter @JonAPrior.