ph question

I've had my tank for a little over a month. In the beginning it was topless which caused a fair amount of evaporation. The ro water brought some things down a little bit. Ever since the beginning my ph has been about 7.8. One time I tested it after having the lid on it for a while and it was 8.2. I don't know why. Then it switched back to 7.8. During the time that it was 8.2 the only changes were the lid was on and the temperature was 80 to 83 degrees. I have used petco's seawater which has a ph of 8.2 and with the exception of my magnesium (which is now 1230 and slowly rising from water changes) everything else is normal.
Some people have suggested that dissolved oxygen is low in my tank. The new tank is 10 gallons with a 75 gph filter on it. I am getting a skimmer for it but it does not have any way to get air into it (it is a nano remora). Even if I wanted to I couldn't hook it up to the air outside in my apartment. Water flow is at the surface so there is surface agitation. I have had an open top which didn't change the ph and currently it has a glass cover which covers about 90% of the top.
I run a filter pad and chemi-pure blue. The temperature is currently 77 degrees. I do 25% water changes once per week. I don't have any kind of top off. My nitrates read between 0 and 5 and the phosphates read none to little (although it is the api test kit not a low phosphate test). Salinity is 1.025.
Does anyone have any ideas about how to raise it?

 

Thank you for the responses. I've heard people say not to chase it. I just wondered if I was getting a lot of algae because it was low. Also, I wanted coralline and all normal processes to happen in the tank. I forgot about the bubbles inside the skimmer. Maybe that will help. Unfortunately, I can't open my window (although I may be able to do it at night) because its hot out and if I have the air conditioner on with the window open it can cause the air conditioner to freeze up. I haven't used ph additives because everyone has said to stay away from them. I know what you are saying abower about petco prices. They are high. However I think the seawater is pretty good and my tank is small enough that it is easier and more cost effective to get natural seawater. I think the water comes from catalina water company. I have dosed kalk before but I don't have much evaporation now and it would be raising my calcium and alkalinity unnecessarily. My parameters are ammonia 0, nitrite 0, nitrate 0 - 5, phosphate low as far as I know, calcium 460 alkalinity 11.5, magnesium 1230, temp 77 and salinity 1.025

 

Unfortunately my funds are kind of low at the moment. I do use chemi-pure blue which has something in it like purigen. I'm not sure if it removes phosphates. I also use filter floss.

 

For the water I pay only $10 a month for it and it is shipped to my apartment. It is the same every time, has the same parameters as natural seawater, it also has many natural things in it that come from the ocean that you don't get in mixed water, none of the uneven balance of things or lack of things as in salt, don't have to worry about impurities in ro water or salt, don't have to worry about salt drying out, don't have to replace ro di filters. There are a lot of conveniences to using petco's water. I have a small tank so it is not extremely cost prohibitive.

 

The tank has been up about a month. Yeah, I buy online and get a discount and then if you buy it through the store you can get free shipping. Actually, I made a mistake. It ends up being $20 per month. I use 5 gallons every two weeks.

 

I think they call it imagitarium seawater.

 

Yeah, it could be. I've had a couple of lights on it which could be part of the problem too. Some intense, some favoring white, green and yellow spectra and some with power compacts that were supposed to be new but maybe were old. The rock I got was cured manado from premium aquatics. Everything was in a biocube 14 up until a few days ago when I moved it to a jbj rl-10-fp. The lighting, flow and filtration is different on the jbj so I'll have to see what happens. It is less intense than the two other leds i've had and can't have old light syndrome so we'll see.
Currently I have a clownfish, long tentacled anemone, green star polyps, emerald crab, peppermint shrimp, astrea snail, three nassarius snails, two blue-legged hermit crabs, a bristleworm, copepods and amphipods. I had two clownfish in the beginning that got sick with brooklynella and died very quickly and a sand sifting star that got stung by the anemone, the peppermint shrimp ate two of its legs and it died. I was thinking of getting a mexican turbo snail but I don't want him to starve.

 

I feed mysis shrimp, marine snow and sometimes some shrimp for the peppermint shrimp and the anemone.

 

Yeah, I usually only put in a half a capful every one or two weeks for the gsp.