Losing weight but body fat percentage is going up?

You're losing nothing but muscle, man.

Either that or your scale doesn't work.

Without strength training to keep your muscle, you may be losing muscle mass. I can't say for sure, but that may be what's happening.

Have you been staying well hydrated? Those body fat scales aren't very accurate, and the readings can change if you are dehydrated. If you have been increasing your exercise, have you also been increasing your fluid intake to counter what you lose in perspiration?

Combination of notorious inaccuracy of those scales, and math.

Even IF you assume the scales were 100% accurate (and that's a GIANT "If")

You start at 200 lbs, 25% BF (just as an example). So you have approximately 150 lbs lean mass, and 50lbs of fat

You lose 10 lbs - of which 2 lbs was fat, 8 lbs was lean mass

You now weigh 190, with 48 lbs of fat, yielding a BF% of 25.3%

Don't go into a panic quite yet. Let's tackle this from multiple angles.

What are you stats? Height, current weight, target weight, RATE OF WEIGHT LOSS, are you vegetarian?, grams of protein you've eaten on average during the past 7/15/30 days?

What do you think your bodyfat % is, and what is the % difference that the Aria is showing you? Is the aria showing a 0.1% difference or a 5% difference?

Have you reset the Aria recently?
(remove the leftmost battery for a second or two, it will show you your wifi name and ask you to tap to change; if you don't do anything, the next time you step on it will perform the "hi-step off-thinking" full calibration routine; probably take an additional 2 readings in a row at that point).

Are you weighting yourself in a similar state? (preferably without having consumed anything and after eliminating and not wet from the shower and at relatively similar times during the day)

Can you afford to invest in a more reliable method of bodyfat estimation than the incredibly flawed bio-impedance analysis scales? (hydrostatic weighting, DEXA scan, Air-Displacement Plethysmography, depending on where you live price and availability may affect your choice).

Also, make sure you are measuring at the same time every day - first thing in the morning post-bathroom, pre-breakfast is best.

I have an Aria as well. Something I really like about it is that I can link it to trendweight.com - it will show you your overall trend in weight, body fat%, lean mass & fat mass.

Fluctuation is normal, you're correct to focus on the trend. Give it time, and don't make drastic changes too quickly. Losing some muscle while on a caloric deficit is almost inevitable for someone who is already in decent shape. People who are very over weight and/or those without much muscle (those who haven't worked out in years, or ever can absolutely burn fat and gain muscle at the same time with diet and exercise. The leaner you become the harder it will get to do this.

If the only exercise you're doing is cardio (running) there is a good chance you could be losing muscle. Without weight training you are basically telling your body that you need to be a lean-mean-running-machine. It will happily respond and become more efficient by shedding off some of that heavy unnecessary muscle (along with the fat). If your interested, try researching type 1 and type 2 muscle fibers. One is for endurance (slow twitch) and the other for power/strength (fast twitch). Running doesn't require fast twitch muscles (as much) so those may get cannibalized to make the running process more efficient.

Apart from weight training, make sure you keep your protein levels up (in the area of 1 gram per pound of body weight IMHO). I've read studies where high protein diets significantly reduced muscle loss in dieters even in the absence of weight training.

Lastly, be patient with your weight loss and shoot for no more that 500-1000 calorie per day deficit. The longer you take to loose the fat, the more likely it is to stay off and the less likely you are to loose significant muscle mass in the process.

One more thing about the fat percentage. If you're using a scale (or handheld) bioimpedence device (one that uses metal plates to send electric current through you) be mindful that these are fairly inaccurate and best for gauging trends. Try to take measurements at the same time of day and under the same conditions (hydration level, time since last meal, etc.). If measuring through your legs (using a scale) you may get significantly lower (and inaccurate) % readings after a leg workout (such as running) because all of the extra blood in those muscles (sometimes its fun to do it for a moral boost though :-) ). If you've been working out for a while and getting leaner, see if the device has an "athlete" mode. The calculations are based on averages taken across a sample population. So the further you are from the average (whether fit or overweight) the less accurate the calculation will become.

Hope that helps. Good luck and keep up the hard work!

Too much cardio, not enough weight training.