Need help getting my tank on track please

[Bugg_zy]

My tank has been looking worse and worse. I walk by, glance at the PH and during the day it's been reading 8.0-8.1. I take the alk/dkh reading twords the end of day light cycle and get a 9-9.5 using salfert, and a 8-8.5 on the elos. So I got up in the middle of the night last night and low and behold 7.64 :squigglemouth: I live in a tiny mobile home and had low PH during the winter but not this low. It would never go below 7.8. I assumed wrong in thinking summer is here, the doors and windows are open, and my ph would be even better. At night though the place is more shut in. I live in a state that running an outside line to my skimmer is not going to work. Recalibrated PH probe a few days ago and it's .02 off from test reagents. The only thing I can think of to combat this is adding a fuge some how but up for suggestions.
Tank info:
75g bare bottom w/100ish pounds of rock
SWC skimmer(been having issues dialing it in lately, I get it there, clean it, then it overflows by the next day)
4 bulb ati T5
30L used as a sump, low flow through it with a mag 5, about 300gph going through the sump(guessing)
3 koralia power heads 1 750 the rest 3's with one tunze
2 little fishes reactor w/gfo (about 3/4 cup)
brs carbon in a mesh bag
Tunze ATO with kalk added(when it kicks on PH rises about .3 for a few mins in the sump(low flow)
I change the water about every 3 weeks using a 5 stage ro/di from brs and use the brute trash can to hold water before the change
Reef Crystals salt (I let it mix 1-2 days before the change)
This tank has been a nightmare since it was set up, it's had every algae know to man, currently it has a little bit of HA and I am guessing I will be picking bubble algae out for the rest of it's existence.
0 phos and nitrates(hair algae eating it up I am guessing)
cal 420, mag just over 1300
After battling HA this long(since a few months after the tank was up) I have pretty much narrowed it down to a decent sized chunck of my live rock. I noticed it really grows on this certain type of rock I have, and barely grows on my other type. I am trying to swap out the bad rock as money allows but due to a surgery and a car accident funds are tight right now. I am gonna go the the LFS and hopefully they will have some macro algae to sell me, looking for suggestions as well if you think I need to add substrate as well to a make shift fuge or if macro alage will be enough. 300gph will be going through the fuge section, only place I can but stuff in my sump is the section the return from the tank dumps into.
I am up for any advice you guys can give me. Thanks for taking the time to read my post :nerd:

 

[spscrazy]

do you let your ro water aerate for 24 hours before using it that made a difference for me also how much kalk are you using for 1 g ro water & do you drip at night aerating for 24 & dripping at night worked for me dang alaska & a trailer??? you are tougher than me!!

 

[Bugg_zy]

ro/di sits in 5 gallon water jugs untill used, no airation and capped. I use a salt bucket to hold the Kalk top up water, I just fill it up as needed, mix a heaping tbsp of kalk in a pitcher of water and add it to my top up water. I make sure the tank is topped up a little bit before doing this so freshly mixed water does not get pumped in. Kalk is added whenever my ATO kicks on around the clock. PH of ro/di after sitting is 6.5ish before adding the Kalk mixture. I am going to make up some new salt water tonight and test it's ph tommorrow.

 

[stedfast82]

I would put some substrate in now. You are haveing trouble any ways .I think you haven no substrate could be just it my 2 cents

 

[spscrazy]

you should aerate the ro water before using it to off gas it makes the ph more stable from what I have read you should have the stored ro water circulating (I do) some substrate should help also

 

[Bugg_zy]

I have about 30 lbs of carbi sea I could add, I had a thin layer when I started up but it just acted as a detritus trap around the base of the live rock. I see folks like wwc have amazing tanks bare bottom but I know not every tank is the same and they may have substrate elsewhere in there system. I have some corals I can trade my lfs for credit so heading in today to grab a few peice's of LR and hopefully some macro algae. Also I am going to rinse off the 20lbs bag of carbi sea(special seafloor grade) and add that to my fuge section(guessing I will want more). Thanks so much for the suggestions and please keep them coming. Hopefully by the end of the day I will have a a fuge going and will just have to wait and see what kind of effect it's gonna have. Also I am going to mix up some water as stated like I always do then ph it. I use an oldschool power head in the brute can so after I take the first ph reading I am going to hook up an airline to the powerhead, let that run awhile then check the ph again. Question...should I buy different grades of sand/gravel for the fuge or is the stuff I have ok? Gonna have about $250 in store credit to work with.