Glass Top or no? 'oh and help with salt please

Right now I have an open top 75 gallon with two 150 watt halides and I have one fan that I got from target and stripped down to fit the hood. Now, with that fan my water evaporates so fast that I'm making new salt once a week which can get expensive over time. I have a glass top that i used to use but was told was unhealthy for my tank to have. Anyone with either setup? which is preferred? Also, when I mix my salt for the evaporation I cant get the salt mix right and my salinity will change. How do I keep it the same? I use instant ocean and 2 1/2 cups per five gallons for regular salinty when I do a water change but i dont know how much to add

 

Make new salt? You do not replace evaporated water with salt water. Only H2O evaporates. Any impurities that the H2O contains is left in your tank. Top your tank off with fresh water. Your salinity must be through the roof.

When you do H2O changes top off you tank and let it circulate for a few hours. Then remove how ever much h2o you want to and replace with the equivalent amount of new salt water.

Since you are using metal halides leave the tops off the tank.

 

+2 Better check the tanks salinity quick. Plus bring it down slow if it is high.

 

yup, dont use SW in top off, only fresh water thats also why you cant get the sg to match in your tank. evaporation with fan is normal and it seems your at a normal rate of evaporation.

leave glass top off as i have read it can filter wanted spectrum from MH. if you have jumpers in your tank get some plastic chicken wire and make yourself a screen over the top (there is a thread somewhere in the DIY section). also be careful with too much evaporation as it can damage your house but it does not sound like you are loosing that much water (~1.5g a day for 100g tank).

to correct your sg that is probably pretty high by now using your top off method, do daily water changes of only 1-2g fresh water until your back down to 1.025-27.