My snails are acting strange

Hello,

I hope any of you can help me out on this one. I have 10 snails in my 20gal tank. Just with in the last week most of them started acting weird. 5 or 6 of the ten are lying sideways and not moving. My temperature is between 76.2 and 78. At night the temp will drop to 75. My pH is 8.4. Tested for nitrates and it is 2.5. I am going to do my every two week water change tomorrow. Do you all think it is the nitrates causing problems? This is the first time that the snails have acted this way. Could it be a temperature problem? Do you all think I should get a chiller? The kitchen in our house is large. I have the tank in dinning room area of the kitchen next to a window. The back glass of the aquarium is covered with a plastic back ground. The kitchen and dinning room area, which are one are the warmest areas of the house. I don't have another area where I could put the tank. Let me know what you all think and suggest.

Thanks in advance to all.

 

some snails cant right themselves you got ot do it for them lol.

when mine fall over i have to stick my hand in there to flip them up

 

Could be the hermits hasslen' them too. Sometimes they will get bored and attack the snails just for the fun of it.

TJ